If anyone has a transmission on the shelf, remove the vented bolt and tilt the tranny over so that the drive gear slips out. It isn't retained in there by much. I think it has a boss on the bottom end that locates it in position inside the case.
If you remove the speedo cable, the top end of the gear is no longer held in place against axial and longitudinal loads. The gear is still driven but is able to move out of its engagement zone. I don't like that situation.
What is the drawback if you remove it? Are other components that are lubricated in there by the splash of that gear?
Wish I know more about the innards of a 5 speed BMW gearbox.