I assume yours is a genuine Quattro? So it'll be the 180PS (177bhp) 2.5 V6 TDI (same as mine), they are normally pretty reliable, but sadly not as reliable as the 1.9TDI... but as with all these things: it depends on wether the car has been well maintained. Most of them seem to be running over 150k miles (250,000km's), at which stage they seem to need a new clutch and often a new turbo. There's somebody on one of the Audi forums who's done about 260k miles (430,000km's) and he's taking it up and down the country at 140mph every week.
Key to keeping it running: regular oil changes and then make sure you get the cambelt done whenever it's due and make SURE they do the waterpump at the same stage.
The thing that's most likely to go on yours is the auto gearbox... they're usually pretty reliable, but I think there's some issues/debates around oil changes on them (AUTO owner please step in here!)....
No worries: I took it as the compliment I assume it was intended as
I agree: an S-Line is a Sport spec with some make-up... although I refer to it as "war-paint"
I would HAVE to agree with that, I just didn't tick all their options (well, I took off the Alloy Reps and door sills and it nearly halved the price): but it is always better to buy the spec you want, rather than tarting up a lower spec car (even if it is only applying the same "make-up" that's on the S-Line, the fact is it will ALWAYS say "Sport" on the V5C, so never worth the same).
The problem was that I needed to get a car that could cover a fair few miles soon-ish and I only had enough to get an early Sport spec: I wasn't even close on the 1.8T / 1.9TDI Quattro S-Lines... plus they're not that common, so decided to do it in stages: besides I really wanted the Quattro and prefered the 2.5TDI's meaty mid-range grunt when cruising, so that ruled a genuine S-Line... TBH, if they'd just colour-coded the lower bumpers out the factory, I probably would never have bothered with the S-Line bumpers.