Do it do it do it do it do it
D2 is the best!
That one doesn't appear to be a final edition as it's plain silver with black leather. The silver FEs were Avus Silver which is darker and has a bit of a purple tint, and afaik they all had red or purple extended leather. Its probably 'just' a reasonably well specified late model S8 - still a very nice car though!
At 140K the timing belt definitely needs doing (including water pump and tensioner) if its only had the one in its life. Frankly, its better to get one that needs doing rather than one that's just been done on the cheap because then you can make sure its done properly. Also the cam chain tensioner pads will need doing asap so its worth combining both jobs. The gearbox will have at most 50K left in it, but that is the price you pay for a D2 unfortunately (its totally worth it!). If it drives nicely with no clunks or squeaks then it'll be a case of keep changing the oil regularly and hope for the best. I've had one to 200K, but there aren't many that make it past that.
However... the '12 months MoT' isn't worth the paper its printed on. The lateral G sensor fault mentioned in the listing will cause the ABS warning light to come on, which is an MoT failure. If the tester has 'overlooked' that for 2 years, what else did they miss? The sensor is under the carpet on the passenger side and needs the seat removing to get to it. Our sponsors should have them available so not too traumatic to fix, but it does make me wonder about the rest of it. There's not a hope in hell it's getting 32mpg on the motorway either
24-26 usually. Maybe 28 hypermiling with a tail wind.
Key problem areas are water ingress (well documented) and rust on the subframes and power steering hoses in the passenger side wheel well. These can both be 4 figures to fix properly. The front subframe rusts out just behind the driveshafts so be sure to check that - jack it up a little with full lock either way to get to the problem area. The Brembo calipers are problematic too - make sure it doesn't pull to one side and that the paint on them is in good order. They are expensive to refurbish.
Given the dodgy MoT and the maintenance it needs I think the price is a little high. You're looking at probably £6K all in for the jobs which are obvious, but I'd always say budget at least £1-2K for other random things which need fettling which puts it at the top of the market for any D2. If the body is immaculate then its worth considering, but I'm not getting the warm fuzzies from it because of the MoT.