If the diagnosis is correct then the VB
is a good repair. The more common problem in BMWs is the harness, which is not that expensive. Unfortunately there are a number of other causes for the "limp home" condition including both internal problems and external electrical.
If your problem is external electrical the new tranny won't help. I wrote an article on BMW trannies. It probaly won't help but if you are interested it can be viewed at: