Never been a big Audi guy, but all of my "car friends" are big into VW/Audi leaving me as the sole BMW/Porsche guy. I really just am not a fan of AWD, even when implemented as well as Audi does (considering the price).
That said, I have a lot of second-hand experience with the 1.8T, 2.0T, and 2.7T motors in particular.
The 1.8T is notorious for sludge buildup IME, and I have more than one friend who thought their motor was in great shape only to up the boost and have oiling issues grenade the turbo('s).
Since I have had such great results with Redline, on and off the track, not only for wear reduction but for cleanliness, I have recommended it to 3 of my friends who have Audi's. A B5 S4, B5 A4, and a B6 A4.
Every one of them showed significant improvements in cleanliness of the valvetrain and combustion chambers after 2-3x mid length OCI's (changing filter 2x each).
I would highly recommend trying it, as with a turbocharged engine like the 1.8/2.0, buildup or poor oil temp control (especially hot spotting) is one of the biggest reasons for the cars' notorious "regular maintenance turbo replacement".