The Audi S8 is a fabulous piece of kit, but was a very expensive car for its day and that means a lot of electrical systems are fitted. It's these that often become unreliable with age, as there are so many connectors and multiplugs that can become corroded, or brittle wires that can break. The 4.0-litre V8 engine is generally pretty robust – but the air suspension system can be problematic. You shouldn't go looking for the cheapest car on the market as it's bound to have issues, but if you find an example with a good maintenance record and from a caring home, then there's every chance you'll end up with a very special modern classic.