Something else strikes you about the cabin - the odometer reads just 47,120 miles. But the thing that you can't see through the RS's lightweight glass is that this particular car has just the single, famous owner recorded in its logbook - British ex-Formula One driver and television commentator and motorsport pundit, John Watson.
Northern Ireland-born Watson is an outspoken and entertaining raconteur and is as passionate about his Porsche now as he must have been when he first bought it back in early 1974, from Paul Michaels at Hexagon Highgate. Watson was performing driving duties for Hexagon's motorsport operations and as a consequence spent a lot of time at the north London Porsche dealer.
"At some time in my journeys up and down to Hexagon I spied 'my' car and lusted after it, principally because at the age of about nine, at a very famous road race in Ireland called the Tourist Trophy, I first set eyes on a Porsche, be it a 356 or a 550 Spyder; in fact both were there. There was something about the Porsches, the look, the sound, that just did it for me: forget Aston Martin, forget Ferrari, forget Jaguar.
"And then the opportunity arose to trade in my first road car, a Ford Granada automatic, with seatbelts and a sunshine roof, bought as the first tangible sign of my being a professional driver. I went to Paul and asked if he'd accept the Ford in part-exchange, with the balance to be settled by him deducting money from my wages. It proved to be a deal that worked out advantageously for him.
"I acquired my 911 in about March of 1974. It became my day-to-day road car. At that particular time, as well as driving Formula One, I was driving Formula Two for John Surtees and doing some sports car races for the likes of Chevron. And frequently if you're going to the northern end of Europe, say Hockenheim or wherever, I'd drive to the venue. Part of the purpose of having a lovely car like this was to do European trips. And that's what I did, primarily in '74, racking up roughly 20,000 miles in one year."
"When I take it out these days I still think what a fantastic car this really is," he enthuses. "What the 911 does is exhilarating, you're getting a massive adrenalin hit. The beauty of the RS is that if you go out on the roads in this area (Oxfordshire) - and they are not actually brilliant roads - because the car is small you effectively widen the road. The RS handles well, goes well, stops well: it is very enjoyable."
Not that Watson is stuck in yesteryear; he has a C-class Benz diesel as his daily driver, and manages to keep his eye in with modern sports cars, too. "The latest 911 Turbo is almost unimaginably quick," he says, "while the new McLaren MP4-12C that I drove recently at Silverstone moves things on to an even higher level. As road cars, those two seem like brain damage to me!"
Though in awe of modern supercar performance, Watson also sees limitations with both the extreme level of that performance and the sheer size and weight of the cars. Especially when it comes to trackdays. "In theory, trackdays are brilliant for those people with high performance road cars," he reasons. "But, if I had a really nice road car, the 997 Turbo, for example, I wouldn't want to take it on the track.
"Through the work I do with broadcasting, I drove a Nissan GT-R, which is a phenomenal car, technologically mind-boggling again; it's exceptionally quick, handles extremely well, but it's a big, heavy car. Nissan themselves do passenger rides for VIP guests with the GT-R and when the drivers have done their runs, the transmission temperature - the car has a gauge - is higher than Nissan recommends as a safe limit.
"Yes, the drivers are giving the car a hard time, but it's only for one lap at a time. It just goes to show how marginal a car like that is between how it performs on the road, where you would never get to that threshold, and going onto the circuit and nailing it, for a lap out, a flying lap, then a lap in."
Mind you, the ex-F1 racer isn't so affectionate about purpose-built race tracks; the sheer pace of modern open-wheelers requires circuits that are devoid of character and atmosphere. "I've driven an A1 GP car around the Shanghai circuit, and from a driver's perspective it has got exceptionally challenging sections - it's a big balls circuit in some places - but what it lacks is personality.
Watson also wonders if modern electronics in Formula One are more of a hindrance to competition than a help. "Valentino Rossi has been bemoaning the introduction of traction control and the like into MotoGP - it has made it possible for riders of lesser talent than Rossi to win races and championships. And the same may be true of Formula One.
"Has technology really helped us? If Sebastian Vettel was in an HRT would he be world champion? Would he have even won a grand prix? No. Would we be lauding him as the next great German driver? No. The fact is that he happened to be in the right place at the right time. Because he is a good driver: the reason Vettel is in a Red Bull right now is because he came through the system and the 'talent' and the team recognised each other. They're not going to put a no-hoper into a Red Bull."
He takes me down to the reservoir in the RS and his smile is quick to appear. The car feels solid, the dynamics tight, the engine lusty, sharp and urgent; our ex-racer doesn't spare the horses and seems to relish even the briefest outing in the car one senses continues to light his fire, and which will never leave his care.