check the bearings on this shaft as well. I found the rear bearing on the shaft had failed and caused the bulkhead and cover to melt a bit, which threw out the mesh. Bulkhead could be cracked as well. I had no problems after replacing bulkhead and cover.
I would guess that the transmission input shaft is bent (part # 7786X - Input shaft, transmission (cush drive)).
This is the shaft that the spur gear is attached - your problem is definitely rated to the spur and not the motor shaft.