Hi
Worst case could be the clutch gone, whatever - the box would have to
be taken out - best advice is got transmission specialist.
I have 740i 97 selects false neutrals - bm dealer quote 4 - 5 k to replace, cost 1100 for a complete rebuild with a torque convertor
and full electronic set up.
The guy who did job also sub contracts to the BM dealership so
there is a profit here somewhere !!!
Regards.