I'm going to share my experiences here to give some balance.
I had a late '99 facelift QTS which I bought back in '06 with 40k miles on it.
It was supplied and serviced via my main dealer (I continued to have them service it) and had 1 previous owner. I think this was key to my ownership experience.
Parts that failed:
Thermostat - symptoms were the coolant temp gauge that would sometimes fail to register after a long drive, but start working again after restarting the car. New thermostat fitted by dealer, under £60.
Water got into the wiring loom this yr after having front discs and pads replaced. Brake warning light would show up when it rained. Fixed by dealer FOC. To give you an idea, the price to replaced front discs and pads was just under £200.
Oil pump (sludge inthe oil pickup) - fixed under warranty
Umm that's it. My LCD screen had full pixels, my stereo worked and the clutch was the original one and is still working fine at 70k.
Things I didn't like:
Steering was dull (like most if not all audis)
It had half leather sport seats that I didn't find that comfy on long distances - i bought some RS4 recaros but never got round to fitting them.
Factory stereo was rubbish.
Things I did like:
The looks - a handsome car for its age.
Build quality - no squeaks or rattles, far better than my simarily aged E36.
The 4wd - fantastic grip come sun/rain or snow.
Things I changed in my ownership:
New sport shocks with H&R springs at 60k
Full Miltek exhaust and downpipe
CustomCode remap at 60k
18" BBS alloys and Falken FK452s
I was so confident about the car's reliability, I sold it on to a good friend recently. I get a lift in it every other week and miss it tbh.
Relentless, didn't you previously post on Audi-sport.net under 'Bong...' something? I remember your posts and your hassles. Iirc you only had it a short time and I thought at the time that you'd bought a fairly bad example. Apologies if this is someone else.