Number 1 Do not take this lying down. Write to the CEO of BMW USA mark the letter "Private and Confidential "and tell him in no uncertain ways how upset you feel in that the Beemer has let you down just out of warranty.
Number 2 If you get no joy contact the ZF gearbox company in the USA and ask them for your local repair agent. Get a quote from them because I guarantee that the BMW garage would take your gearbox to them to repair anyway and would then just double the cost and charge you.......... I have seen this and its a great source of amusement to the BMW service people
Believe me I have had a host of problems with BMW 740 engine and gearbox combo and the local techies here havent a clue, any problems they just swap components hoping to solve the problem or they take the car to a subcontractor who knows what they are doing......
The above is now why got rid of my BMW 5 series and I now drive a Jaguar and am loving it...........
Cheers,
Tony
