Hi
I've had a 2002 Audi 2.5 TDi Quattro from 2004 and it's now up to 180,000 miles now.
The automatic Quattro's (permanent 4 wheel drive) all have a conventional 5 speed automatic gearbox with a torque converter and it's meant to be fairly robust. It's the front wheel drive non-quattros that have Audi's CVT 'Multitronic' that's prone to a lot of failures and is definitely one to avoid.
A couple of things to be aware of. The cambelt change (at about 80K) can be expensive as you really need to get the water pump and tensioner changed to and to carry out the work they have to take the front end of the car off! Audi typically charge about 700 to 800 pounds for this depending on the dealer. Third party garages are about 500 to 600.
The thermostat is located behind the cambelt so if the thermostat goes (mine locked closed) then you will probably need a new cambelt too so for the sake of a few pounds it's best to get that changed at cambelt time too.
The toys in the car vary a lot depending on what the owner specified off the options list. Mine is lucky enough to have the really nice sports seats with electric lumbar support and adjustable bolster. They are very supportive when the car is cornered hard (and the 4 wheel drive gives lots of traction).
I've been really happy with mine and hope it lasts for many more years.
Quite a front heavy car but lots of grunt and effortless to drive.
Ox-Xen