Sorry I've not been replying, folks... I've been busy driving Audis!
There is another S8 on sale locally with similar mileage, so I called the garage and asked to take a look. The seller was busy with another customer, so he let me snoop around the car by myself, which was great because it let me find my groove.
I plugged in the VCDS and did an auto scan and, while it was running, poked and prodded around the interior pushing every button I could see (and even discovered a few I hadn't).
This one was a 58 reg, so it had some subtle differences. I'm sure some are down to specification and others are down to the model year. The gauges did a needle sweep on startup which I don't remember seeing on the other one, which was a nice touch. There was also a brolly holder in the boot (I know how much you guys value a brolly holder). This one had a sunroof and homelink and, although it wasn't working, I found myself staring at it longingly.
To cut a long story short, the interior electrics (except the sunroof) all worked fine, right down to the electric headrests.
He also had a 3.0 TDi A8 there and I took some time to snoop around that one too, including starting it and moving it around the car park.
Then, a surprising thing happened... I'd checked all I could with the car stationary - the bootlid worked, the engine oil smelled the same as the other car, there were no obvious signs of body damage. The seller came over to me and asked how it was going and whether I'd like to take it out for a test drive. When I replied that I would, he first said he would take the other customer out first, then changed his mind and said I could take it out by myself!
I tried to control myself and not do starjumps, but I found myself on my own in an S8 to test. This made the world of difference and, suddenly, without worrying about time, my passenger or the deluge, I was able to calmly test the car.
All I can say is that it was a revelation! The car itself (as you all already know), is a lovely thing to drive. I was pleased that it had the same snatchy take-off as the other, so I'm no longer worried about that. Thank you to whoever pointed out that the steering was dynamic - now that I knew what to look for, I get it completely. It felt just like the last one and even hissed slightly on full lock, right on cue.
There were two major differences in the way these two S8s drove:
1) This one rattled and squeaked over bumpy surfaces, where the other one felt solid.
2) The brakes on this car were scary! As I drive such an old car, I'm accustomed to brakes that are... leisurely. When I got into Thursday's S8, every time I dabbed the brake pedal, it wanted to do an emergency stop. This one slowed down only a little better than my own car, so I had a nasty fright the first time I wanted to slow down for a 90 degree bend!
When I got back, I tested the suspension (the battery wouldn't let me do it before without the engine on) and it raised and lowered much slower than the other car. The seller had another customer turn up and I could feel he was beginning to feel stressed by juggling all of us, so I thanked him and left before the second VCDS check.
All in all, I think I gave the first car a much harder time than it deserved. I think this was in part due to it being my first time driving one and partly because of the less than perfect circumstances in which I drove it. I'm going to call the seller and ask to take a second look tomorrow, when I can hopefully get a little more time to check it properly and give myself enough peace of mind to say 'yes'.
To those of who who have kindly offered to swap your standard exhaust for the Milltek, thanks very much and if I buy the car I will consider it, but I'd really like a new exhaust if I can stretch to it. If so, the Milltek will certainly be going on sale.