Occasionally I lose reverse gear on my 2008 Audi A3 Quattro 2.0T DSG. In reverse position the car will not move and will only rev to about 1200rpm. The only way to cure this is to turn the ignition off and re-start the engine. The car is still under warranty and been back to the dealers 3 times, but they cannot find anything wrong, I now have complained to Audi UK who have taken up the case but still want me to take the car back to the local s******s. Any ideas?