I have seen a handful of belt failures mentioned over the years on the C5 (A6) board, which in its day probably had 5x the message traffic this one does. Change interval on C5 RS6 was every 30K by the way. And, Audi Care used to go 75K instead of 65K, until I guess someone woke up that they were covering the belt job.
A6 / S6 (C5 Platform) Discussion - Timing Belt or Timing Chain - BACKGROUND My daughter just bought, from a local reputable Audi (new & used) Car Dealer (Western Chicago Suburbs) a used 2003 Audi A6 with 108,000 miles on the odometer for our grandson. From the pictures she sent me all I can tell is the vehicle is a

Air Cleaner – clean housing, replace filter element l 55K only: except Audi Q7 4.2L and A8 6.0L l 35K only: A8 6.0L only; 75K only: Audi Q7 4.2L, A8 6.0L only; 115K only: A8 6.0L only Ribbed V Belt and Tensioner – check condition and replace if necessary l Audi R8 only l Audi Q7 3.6L, A8 6.0L, Audi R8 only Ribbed V Belt – replace l

Many, many posts can be found here on opinions of the merits of Audi Care - do a search. It's actually for scheduled maintenance coverage for 15K, 25K, 35K and 45K miles services or 5 years (not 4 years) whichever comes first (note the exclusions). If I had to take a guess, pro comments would be about 2 to 1 for non-do it yourselfers.
As a courtesy and for a small fee ($75.00-$90.00), we offer the option of renting an Audi Timing Belt Tool Rental Kit to customers who purchase one of our BLAU Audi Timing Belt Replacement Kits. Our Audi timing belt tool rental program allows technicians to use the special tools required, without the investment. For example, a set of special Wiper blades - Check condition and replace if necessary Additional Maintenance Items Work to be completed Interval Model Application Air filter - Replace Every 40k miles RS7, A8 LWB only Air filter - Replace Every 60k miles All vehicles except RS7 and A8 LWB AWD clutch - Change fluid (if equipped) ymg7861. 420 227 379 36 186 240 96 297 449

audi a8 timing chain replacement interval