if the problem is with the film take-up end I think you are going to find that something internal to the camera on that end is not releasing properly, or is gummed up and binding. Perhaps a bearing that rotates one way but not the other. If the geared drive wheel turns in both directions smoothly when the rewind lever is pushed over, then as you say, it is probably the bearings of the shaft of the take-up spool itself.

I can think of no other way than a disassembly by someone who knows what he/she is doing. Sorry. There are several good repair places in England and Germany, of course, has Leica itself.