I think its Getrag..The trans number starts with a "G" (GS6-53DZ - TJGC)
but also found this ..BMW Trans.pdf
BMW transmissions are manufactured by two suppliers for the US market:
• Zahnradfabrik Friedrichshafen: Commonly referred to as ZF. ZF manufactures both manual and automatic transmissions.
• GM Powertrain - Hydramatic: Hydramatic is a manufacturing division of General Motors located in Strasbourg France. Hydramatic supplies automatic transmissions to BMW for four and six-cylinder vehicles.