Late to this thread, but...
I had 320,000 miles on my '93 A4LD before I pulled it for the V8 swap.
At about 318,000 miles (and I was in California - about 2,000 miles from home) it started slipping. Not a lot, but noticeable, and the temperature rose - and stayed up. Along about Oklahoma, I added 6 quarts of fluid. Apparently, a seal started leaking. I made it home under my own power.
Didn't drive it much during the next several months - then, it got pulled.
Apparently, this long of a life is the exception.
For the record, I changed the fluid and filter every 15,000 miles.