The main thing to watch out for is the timing chain. They can stretch and rattle if not serviced accordingly over the years. Also the timing chain tensioner was considered a weak point in pre 2005 models. This causes the chain to stretch and rattle. Eventually this means poor performance and even worse the timing will go off and the valves will hit, meaning a massive repair bill.
Research the issue on Google and you'll see plenty of info. I read an article from Germany discussing the issue and the fact Audi never accepted it was a fault. However in 2005+ models they changed the guide tensioner and the chain, using one which wasn't imprinted with a logo, which apparently made it weaker.
Start it up and listen to the engine at the side under the oil filler cap. If it's stretched or rattling you will hear a scrapping rotational noise from the chain. I test drove 4 before eventually finding the right one and all but one of them had the issue. Admittedly they were 54 plates although one was an 05 that also had it. Here's a video I took of one I looked at with the noise...
3.2 V6 - YouTube
Good service history is important with these cars, in particular regular oil changes with the correct grade of oil.
Also check for history of the Haldex oil change (for the Quattro) which is due every 40k, as is the DSG oil if you opt for an auto like I did.
Don't be put off by the above but these are the expensive issues that you can avoid with proper research and a good checking over of a potential purchase.
It is without doubt the best car I've owned and driven. It's a superb machine that never fails to put a smile on your face. I opted for a 2007 model with S-Tronic (DSG) and its a beast. The sound is fantastic and the power is there whenever you need it.
Here's a pic of mine...
Happy hunting.... and with respect, you will find great advice from audi-sport forum as noone actually replied to this thread of mine for advice.
