News that the Audi S5, S6 and S7 are set to swap to diesel power inspired the selection of this week's Brave Pill, with this stylish reminder of Audi's long enthusiasm for brawny compression ignition engines. While the new S-grade TDI is a V6 helped along by a 48-volt compressor our Pill takes a more old-fashioned approach to muscle: capacity and cylinders. Despite the passage of 14 years, and the lack of S branding, the A8 4.2 TDI Quattro is barely less potent than its e-boosted successors.
Volkswagen Group went diesel mad in the 'noughties. We know how that ended, of course - with many of the brand's senior executives trying not to drop soap in the showers of Germany's federal prison system. But in the early days this obsession with reducing the corporate spark plug bill resulted in some truly memorable machinery.
The biggest headlines were won by the mighty 313hp 5.0-litre V10 TDI, the deca-pot that did duty in the Phaeton and Touareg. It was an engine bay stuffer which quickly developed a reputation for delivering the sort of maintenance bills a Bentley owner would regard as a bit scary. The Phaeton reportedly needs its V10 dropped to change the alternator.
The V8 is much more sensible. Although smaller and less cylindered, the common-rail 4.2-litre version, which replaced the earlier 4.0-litre unit in 2005, is actually more powerful than the V10. Indeed, with 326hp the A8 was the most powerful diesel engined passenger car in the world at launch and also the fastest accelerating.
In period, it was a proper star. Autocar once described the 4.2 TDI's combination of economy, pace and dynamic security as making it the best car in the real world and that case is still arguable even a decade and a half later.
I was roped into a comparison test featuring a 4.2 shortly after it was introduced, on a particularly cold and wet day in Snowdonia. It was a miserable photoshoot in heavy rain and it was dark before the snapper finally gave up and sent us home, triggering an unseemly scrap for the A8's keys. Somehow I prevailed and remember a proper timewarp experience along sodden motorways at the pace of somebody very keen to get home, listening to the exceptional audio system and with the seat turned to high heat and full massage. Very few cars do high average speeds in poor conditions better than a big Audi with the Torsen differential Quattro system.
The rest of the A8 has aged pretty well, too. The second generation D3 was introduced in 2002 and built on the pioneering tech of the original A8. That means an aluminium structure which was pitched as saving weight, although the V8 TDI still bends the needle of the scales at 1995kg. Air suspension and active dampers were standard and the car's range-topping status meant it was packed with firsts: Audi's MMI interface made its debut here, as did DVD-based navigation, a display screen that motors out of the dashboard, adaptive xenon lights and even the option of a fingerprint system to adapt the car between different drivers' preferences.
While no sportscar the A8 is as agile as it needs to be in its part of the market. Our Pill is the more common SE rather than the slightly firmer Sport, though it still has adaptable air suspension with the ability to offer both acceptable levels of dynamism and a proper limo impression.
Despite its V8-ness the engine doesn't sound that great. Outside the well-insulated cabin there is a tinkly idle and under hard use it thrums rather than produces any sweeter tone. But fully unleashed it can get to 62mph in 5.9-seconds - still impressive - a figure that meant it was actually half a second quicker than the contemporary 4.2-litre V8 petrol.
But economy was where it got really impressive. Big and fast stuff rarely gets close to official figures, but the A8 is an exception. Driven carefully it can beat its official 31mpg combined score, although mid-to-high 20s are more common in everyday use. Still entirely reasonable for something so quick.
Not that this is a car for misers. The running costs of any elderly A8 are unlikely to be small - the pulse-racing frisson of wallet-peril is standard with any Brave Pill. The earlier 4.0-litre V8 TDI frequently suffers from injector problems, but the 4.2 is both tougher and punchier. Our Pill boasts a full history and the owner has reports taking the sensible precaution of changing transmission and differential fluids on what Audi claimed was a sealed-for-life gearbox. Electrical problems and check-outs can strike, and tracking them down requires specialist expertise and often expensive parts. It's definitely a car that is best owned with a generous bork fund.
Our Pill's private plate denies us a forensic look at its MOT history - the DVLA thinks it is on a BMW M6 - but I'd place a modest bet that it was originally registered in Oxfordshire as part of Audi's central fleet. There are two reasons for such deductive reasoning. Firstly the 4.2's forest of ticked option boxes, including power blinds, adaptive lights, soft-close doors and the bangin' (sorry) Bang & Olufson audio upgrade, a 14-speaker 1000-watt system that was a four grand extra in period. It even seems to have the fingerprint scanner next to the gearshift. I'd be surprised if a civilian purchaser would go for quite so much kit.
But the second reason for my hunch is based on pure statistics. Audi registered (and still registers) a huge number of well-equipped A8s for its VIP chauffeur fleet, with up to 200 cars on the go at once. Journos affectionately refer to these as "Zammocabs", named after Audi's former head of PR John Zammett. These cars lead an easy life trundling A-listers to glitzy premieres, or sometimes Z-listers to the TV Quick Awards, and are dropped onto the used market with serious discounts after a few months of gentle use.
Despite nearly 140,000 miles our Pill seems to have been properly looked after with a recent service and inspection of the air suspension. There are cheaper ones out there, although most will be the less loved 4.0-litre. The price seems fair considering the sheer quantity of car on offer here. With an age-hiding plate, a rear bumper respray and a mate persuaded to don a chauffeur's cap for an evening it could still turn you into a minor celebrity.