The owner's manual for the 2.7T/3.0 calls for the TB at 105k, but conventional wisdom is 75-90k. I opted for 90k and 185k. In your case, based on age vs mileage, I would consider it as a safety measure. I agree with all the preventive maintenance recommended by bigdadi and follow it for both my Audis. You can add changing the brake fluid, which should be done every 2 years regardless of mileage.

I bought a 2003 A4 3.0 MT6 for my daughter and the engine has been solid. I did have the cats replaced under warranty at 79k, and the cam position sensors. Did the TB a little early at 85k because she was taking it 600 miles to college (indie shop charged $1150 vs $950 for the 2.7T). The only unsolvable issue is the clutch pedal sensor has been replaced and still throws a code, but you have a tip so not an issue. The engine is currently at 94k and does not leak nor lose oil between changes, and I do use Mobil 0W-40.

 

I also had 2 Cam-Position-Sensors on driver side replaced 1 month ago ... car is now 136k no fluid leaks.

23.5MPG highway, 20.3MPG city/hwy combined.

Others replaced: Coolant Temp Sensor (Pax side firewall), Aux Cooling Fan (Pax side), Power Steering sys hose clamps (loose clamps let air sips into the P/S liquid), Flex pipes, O2 sensor spacers. Nothing wrong with the cats, just Audi ECU spec is too narrow to throw a code.

 

Just a guess ... the indy shop did the liquid change ... Front Final Drive, Transfer Case, and Rear Final Drive.
OEM P/N should be G 052 145 S2 which is a fully synthetic 75W90 oil

I have B5 A4 maintenance link below ... more or less the same to C5 A6
http://www.vaglinks.com/Docs/Audi/B5...aintenance.pdf