I am certainly not a mechanic. The car just stopped moving forward and I could feel the transmission slipping - like I was holding a clutch down.
The local Audi dealer told me the transmission failed because I did not drive the car hard enough! (Guess I should have tracked the car.)
Thankfully, I did get Audi to pay a significant portion of the repair/replacement of the transmission. I think I paid around $3,000 of the $13,000 quote.....