I have 1999 Audi A8 4.2 quattro with 75k. I had trans problems 8 months ago, so I bought a rebuilt trans. Well it did not last long. Whle driving a rpm start going high and than a car start losing a power and some noise from the engine showed up (like something fall off ). I stoped a car right away. Next morning I started a car and after driving 25 miles/h with high rpm for a mile it went to fail safe mode. I parked the car. When I started again it was not in a fail safe mode no more but all other problems were still there. I get it towed to service and here are diagnosis
17125 P0741 Torque Converter Clutch Performance or Stuck Off
17118 P0734 Gear 4 Incorrect Ratio
17114 P0730 Gear Incorecct Ratio
17087 P0703 Torque Converter/Brake Switch B Circ Malfunction
Needs timing belt kit and they told me over a phone water pump as well but they did not stated that on invoice. I do not now what to do. Please any advice on real source of my problem based on codes.

 

Well buying a used trans for a D2 A8 is a worse gamble than betting against the house playing black jack. From the looks of the fault codes the torque converter is shot, a tech can easilly verify this by looking at the TCC and stall speed using the vag com, but im sure its done. As for the incorrect gear ratio faults, thats never a good thing, especially on a D2 A8. You most likely need yet another trans, or have this one re-built correctly, with a warranty as well. If you are going to do the timing belt, you NEED to do the water pump, tensioners, and rollers along with it.
You are looking at some serious repairs here, probably in excess of $5,000. I would ask yourself if you like the car enough to keep it, or throw it away.