Mercedes-Benz SL (R129) | PH Used Buying Guide
Thirty years old this year, there's still much going for the '129 SL - here's what to look for...
If you want a quality convertible with the potential to take you, the OH and a couple of smallish nippers on a long and comfy journey with the sun beating warmly on your nuts, there's not a lot of competition for the SL-Class Mercedes.
M-B has been building these grand touring sports cars since the mid-1950s, and none of them have been duffers. Which model should you choose though?
Decent examples of the R107 (1971-1989) are now at least £25,000 a pop, and good ones are considerably more. The R230 (2001-2011) is more affordable in its earlier forms, but you might think it's a bit too mainstream and maybe not quite different enough from smaller Mercedes sports cars to give it that true touch of SL class.
Which leaves the meat in the SL sandwich, the R129 which ran from 1989 to 2001. Many believe that the R129's accessible blend of grace and ability makes it something of a bargain. Although you can pay well over £30k for a late Silver Arrows SL500, R129 prices start from as little as £3000 - remarkable for a superbly built car that, when new, cost between £60,000 and £100,000.
How brave would you have to be to dip your toe into SL waters at that sort of money, though? Let's investigate that beard-stroker with this buying guide.
We're lucky here on PH because of the regular presence on these forums of two R129 experts, namely Nick Froome and the appropriately named r129sl. In addition to their freely-granted wisdom, for which we thank them heartily, many R129 owners have reported their experiences on our forums, and the vast majority of them have been very positive.
Remember that last point as we go through the ins and outs of R129 ownership. Our aim with these guides is not to have you running away in panic but to give you a useful toolbox that will help you secure the best car for your hard-earned. By definition, that means we'll be pointing out the car's weak points. This is not to slag a car off or to scare you off buying it, but to give you a clear view on what to look for.
As noted at the beginning, these SLs are grand tourers rather than out and out sports cars. The R129's multi-link suspension was firmly damped but softly sprung, and their engines were refined rather than rowdy. These design features made them ideal for touring and/or cruising - which, when you think about it, is what most of us do most of the time.
The R129 platform was a shortened version of the W124's, and the running gear on earlier cars was also based on the granite W124, which means that R129s are both as tough as old boots and not as expensive on parts as you might think. The R129 is a good bet from a safety perspective too as it has most of the modern countermeasures you'd hope to see - airbags, ABS, stability control, a strong body shell and a pop-up bar to protect you in the event of a rollover - but without much of the electronic drivetrain complexity that can bring down quite a few otherwise good modern cars - like the R129's successor, the R230.
PHers have testified to the strength of their SLs. A large Iveco van ran into the back of one with sufficient force to deploy the SL's rollover bar and seat belt pretensioners. This PHer says he didn't feel a thing and was able to open and close the boot lid and drive the car home. The Iveco was immobile in a pool of water and oil. In case two a black cab ran into the back at a lower speed, not enough to activate the roll-over bar but enough to cave in the taxi's grille. The only damage to the SL was a very slight scratch to the paintwork.
Besides its electrically-operated soft top, every UK-spec first-gen R129 up to the first 1995 facelift had a removable hardtop plus electrically-operated seats, alloy wheels and an automatic transmission. These gen-one cars generally had two-tone paint and orange indicators, although you do sometimes see the latter on later cars, or post-facelift clear lenses on pre-facelift cars.
Folk don't change the bumpers or sill covers on R129s much, however, so if you see squared-off lines in these two areas, along with less rounded door mirrors, heavily ribbed tail lamps, a more hidden exhaust, and the presence of three rectangular vents behind the front wheels (gen-two vents were an elongated egg shape, and there were only two of them) then it's a fair bet that you're looking at a gen-one car. Those 1995-1998 gen-two cars had single-tone paint but with satin-finish lower body panels.
Gen-three cars after June 1998 had a bumper cutout and grey trim for the exhaust, bigger 17in wheels with larger brakes, all-red (rather than orange and red) tail lamps, single-colour one-type paint, SLK-type door mirrors, chrome rings around the instrument dials, and leather as standard. Technically, standard R129 upholstery up to that point was plaid cloth, but the luxurious nature of the car meant that the vast majority of R129s (in the UK at least) were optioned with leather. Cloth R129s are, as a result, very rare now.
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Bodywork & Interior
R129s came in a smashing range of colours. Even the traditionally 'boring' hues like black, blue, grey and silver look great on them. For short periods at various points during the run you could also get Designo colours like Mineral Green.
While we're on the subject of smashing, the powerful and sporting nature of the R129 means that one or two cars will have suffered accident damage. Poor panel fit where the front wing, front door and 'A' pillar come together or any signs of new metal under the bonnet or boot floor should sound alarm bells.
Thankfully, the R129 is nowhere near as susceptible to corrosion as many other contemporary Mercs, but they're not invulnerable and paint damage can obviously open up the door to rust. Check the leading edge of the lower front wing near the bumper, the front wheel arches, door edges, boot lock and rear wing lips. If you're scoping out a car with a panoramic roof, you might find a dod of the brown stuff on its trailing edge, a mysterious phenomenon that fortunately rarely becomes problematic.
Ah, we appear to have reached the hood section. OK, let's do the soft-top first.
To check that your prospective R129 has its original soft top, look for M-B stars in the corners of the plastic 'glass'. Soft top rear windows can split where they fold. Polishing them with the right proprietary product can reduce their tendency to split along fold marks or to come away from the hood, and will also help to remove any milkiness.
If the original hood is beyond redemption, aftermarket items are available, but the plasti-glass on these is somewhat thinner and more inclined to flap at speed. If you're minted, make inquiries at your M-B dealer. They will be delighted to take large quantities of money off you in exchange for a factory hood.
Generally, the R129's electrical system is pretty reliable, but if your R129 lives outside, expensive electrical bits like the roof controller module under the rear seat may start to play up. A great way to speed up the RCM's demise is to spike the battery by jump starting the car, so avoid that if you can.
All R129s came with a hard top, either 'solid' or with a panoramic glass panel. The pano roof was a £6k option when new and is especially worth having not just from a values point of view but because it really boosts the cabin ambience. It's damned heavy though. If you can't run to (or find) one of the hardtop shuttle gizmos that used to be made for it, removing a hardtop is most definitely a two-man job. Once it's off and you've finished leaning on the garage wall and wheezing, pop it on a roof stand to minimise damage in storage.
Moving inside for a much-needed sit down, you'll find plenty of space and four seats, two of which are very comfortable. Ideally those two front seats should be heated and will have a memory function that's linked to the steering column and all three mirrors. The rear seats will suffice for uncomplaining children of a single-figure age, but you only get lap belts and fitting child seats isn't easy. Best to not have children. That way you can fold the rear seat backs down to create a decent cargo area supplementing a boot that is very decently sized for this type of car.
Pre-1998 non-nappa-leather cars had durable perforated seat centres but the seat bolsters did wear. That can be a problem if you're a perfectionist because much of the interior trim for these R129s is now either prohibitively expensive - £1000 or more for a seat cover - or simply unavailable from M-B in the case of (for example) inner sill carpets. A company called Special Vehicle Services may be able to help on difficult-to-find items, however.
Again, if you must have your SL perfect, check the condition of the wooden centre console. If it's damaged, getting a replacement from Mercedes that will (you hope) match the walnut door cappings is another four-figure expense. Top money-saving tip here is to take the console wood to a furniture restorer for sanding and relacquering. That way you're guaranteed a grain match - and a much smaller bill.
Door and dash storage boxes commonly jam or will have snapped-off clips. The adjusting knob for the sliding centre console armrest regularly breaks off, as does the lever on the passenger side air vent. The hinges on the vanity mirror are fragile too. The overhead light panel by the rear-view mirror can become sticky through long-term effects of heat, and sun visors get cracked (ironically) by the sun.
Air conditioning was an expensive option on early cars and was fairly reliable, but the condenser situated at the front of the car eventually fails, as does the evaporator temperature sensor, icing up the evaporator and blocking cabin air flow. Windows conk out too, but show us an old car where they don't.
Luxury features can be pricey to put right. Headlamp wash/wipe motors are famously dicky on Mercs of this vintage, and the R129 is not exempt. Not sure if this is still the case but xenon front headlamps used to be available only from M-B at around £750 a side. Crappy old alarms can drain the battery and central locking failure is not unknown.
Engines & Transmissions
Here's a statement to argue about: the range of engines used in the R129's life was one of the two best normally-aspirated engine ranges (four-cylinder motors excluded) ever.
There, we've said it. Irrespective of your own views on that, here's what was on offer. Notice that on post-1993 cars the badging protocol swopped over from number first to number last.
300 SL (1988 to 1993): M103 3.0-litre inline six, SOHC, 12-valve, 190hp
300 SL-24 (1988 to 1993): M104 3.0-litre inline six, DOHC, 24-valve, 231hp
500 SL (1988 to 1993): M119 5.0-litre V8, DOHC, 32-valve, 320-326hp
600 SL (1991 to 1993): M120 6.0-litre V12, DOHC, 48-valve, 394hp
SL 280 (1993 to 1998): M104 2.8-litre inline six, DOHC, 24-valve, 193hp
SL 320: (1993 to 1998): M104 3.2-litre inline six, DOHC, 24v, 231hp
SL 500: (1993 to 2008): M119 5.0-litre V8, DOHC, 32-valve, 320hp
SL 600: (1993 to 2001): M120 6.0-litre V12, DOHC, 48-valve, 394hp
SL 280: (1998 to 2001): M112 2.8-litre V6, SOHC, 18-valve, 204hp
SL 320 (1998 to 2001): M112 3.2-litre V6, SOHC, 18-valve, 224hp
SL 500 (1998 to 2001): M113 5.0-litre V8, SOHC, 24-valve, 306hp
Time for some Mercedes engine generalisations.
The 5.0 V8 is strong, grunty and a contender for the title of 'best engine ever made'. The 3.0 sixes are bombproof. For every '280s are gutless' hater there will be a '280s are smooth and wafty' 280 lover.
AMG and Brabus produced their own R129s. Early SL 60 AMGs had a 386hp 6.0-litre version of the M119 V8. They found fewer than 100 UK buyers. The 525hp SL 73 AMG was even rarer, making up around 40 to 50 of the thousand or so AMG R129s built. The 73 used the 7.3-litre version of the M120 Mercedes V12 that went on to become legendary in the Pagani Zonda.
Even the standard V12 R129 was a comparatively rare beast. For every SL600 sold there were ten SL500s.
Back in the real world of SL ownership, many say that the fuel penalty you pay for the 500 over the 320 or the 300 is a very fair exchange for the V8's pace (it's nearly two seconds faster through the 0-60) and sound. In extremely moderate driving you might get a 500 to an mpg figure in the high 20s, but driven with gusto it will be more like 15mpg and will usually return an average of 22-23mpg. It's a fair bit easier to hit that 30mpg mark with the six-cylinder cars, a fact that tends to keep their values high relative to the V8s. There again, you could easily say that you can buy a lot of fuel with the money you save on buying an eight. It's all justifiable using man maths.
Don't dismiss the sixes on character, though. They have their own cammy fizz that's very appealing at higher revs. Opinions are as divided on the SL 280 as they are for every other Mercedes with those numbers on it. They do run out of puff slightly at higher speeds, but hitched up to the slick 5-speed auto they do a perfectly good job 95 per cent of the time.
Common problems on early R129s include head gasket leakage as a result of corrosion. Rarely do they catastrophically pop. Keeping the coolant clean is a good policy: at the very least change it every three years. Another well-known R129 issue is misfiring either as a result of damp distributor caps or crumbly wiring looms in the case of the M104 2.8 and 3.2 engines. Although these later sixes shared the M104 appellation with the early 3.0, they were quite different units. The early 300 SL-24s had mechanical injection and electronic ignition with a distributor, whereas the later 2.8 and 3.2 had HFM electronic injection and three-coil-pack distributorless ignition.
The M112 V6s were more reliable than the older sixes (barring a problem with the crankshaft balancer, which was given to breaking up) but they don't quite have that same hard to describe Mercedes 'feel'.
Faulty throttle body wiring on the M119 V8s will create poor running and difficulties with the ASR traction control system. Blocked camshaft oil feeder pipes can blight the experience but the timing chain and associated gubbins is good for 150,000 miles.
More generically, rattling at tickover may be caused by catalytic converter breakup, and the received wisdom there is to avoid non-factory replacements, which means a bigger expense, but you might be lucky and find it's actually nothing more than a loose heat shield, which is very cheap to sort.
R129 gearboxes are generally tough, especially if it's the four-speeder. The 722.5 5-speed transmission (initially a hydraulic 4-speed with an electrically-operated overdrive 5th) started as an option for sixes from around 1992 to 1996, at which point the 722.6 5-speeder took over. The 722s are perhaps less sturdy than the four-ratio boxes but they are nicer to use, especially on the smaller engines.
Fluid can escape from around the diagnostic connector on the 722.6 5-speeder and find its way along the wiring harness and into the transmission ECU, killing the gearbox's ability to change gears.
General mech tips? Keep on top of the oil quality and change the filters every 35,000 miles. Service the transmissions every 40,000 miles despite what the official service schedule says. Change the spark plugs (12 and 16 of them respectively on the twin-plug M112 V6 and M113 V8) every four years/60,000 miles.
Suspension & Steering
As noted earlier, R129s operate on the principle of long-travel but firmly damped suspension, which with the five-link rear axle makes them a great mix for most British owners.
These Mercs are quite heavy though, especially the V8s, so they do tend to chomp through consumable suspension components. The front lower ball joints and top strut mountings take most of the weight. Rust can hasten breakage of front springs and of the brace support bars.
Freshening up the suspension on an old R129 will restore it to the brilliant level of driving pleasure that the first owners would have enjoyed. At the front, the kit required for this will be new anti-roll bar bushes, which have a life expectancy of around 20,000 miles but are very cheap and quick to install; dampers, and damper top mounts. Knocking in the steering will most likely be down to these ARB bushes.
Rebushing the cross-braces is cheap (in parts costs anyway) and will quieten down vibration at fast cruising speeds. If the bushes at the back end need you may as well get new suspension arms while you're at it.
Lemförder, Bilstein and Sachs all make suspension and steering components for Mercedes and are great names to have on any pattern parts you order. They're available online from all the usual German car part suppliers. As a price guide, a complete 12-part set of Lemförder suspension arms and tie rod ends for the front end will be £350.
Some R129s, and all SL600s, came with Mercedes' optional Citroen-sphere-type ADS (Adaptive Damping System). Inside the spheres, nitrogen and fluid on either side of a diaphragm provide ECU-controlled damping. The spheres wear out and faulty valve bodies aren't cheap to mend, but R129 owners who have fully-functioning ADS really rate the reduction in roll.
Wheels, Tyres & Brakes
To those accustomed to the sharp braking response of modern cars, R129 brakes may initially seem somewhat wooden, but give them some good old-fashioned Wagnerian leg action and even the pre-'98 cars with smaller brakes won't be found wanting for stopping power as long as you change the brake fluid on a regular basis, ideally every two years.
As regards tyres, those in the know recommend Michelins, and specifically Pilot Sports, either PS2s or PS3s. If a car you're thinking of buying is wearing non-premium brand tyres, that's not necessarily a concern from a handling or safety point of view but it could be seen as an insight into the level of maintenance that's been put into the car by the current owner.
Try to find a car with the correct diamond-cut wheels, as the 'wrong' wheels just look, well, wrong.
Conclusion
To conclude, here are two key R129 buying tips.
One is to buy original spec cars based on their condition and, to some extent, on the vendor. Experts believe that an unmaintained or inadequately maintained SL (i.e. one that hasn't been serviced at least annually or every 10,000 miles) is a potential money pit waiting to trip up the next owner. Depending on how long you keep it, a super-cheap R129 can easily end up costing you more than a higher-priced but properly maintained one.
Having bought your R129, here's the second important tip: use it, and don't spare the rod either. Enthusiastic driving will play a big part in keeping it running as the manufacturer intended.
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