Hi,
Sorry but I think I missed your last post on this thread, things have been rather quiet on the lawnmower front with many people doing other things at this time of year.
Next plan of attack is to set up the reel and bottom blade so there is very light contact between the two and see if the issue is resolved.
Also have you tried Simrice's evaluation of the transfer shaft woodruf key wear ?
Cheers,
BB