If you want to pull it open and inspect the trans, probably a good idea, we will need the following to put it back together at a minimum, assuming nothing is wrong internally.
Clutch Nut
Clutch Cover Gasket
Threebond 1207B
Stator Cover Gasket
Detent Spring
Red Loctite
Input shaft Bearing bolts
Detent shaft bolt
Special tool to remove the flywheel
Can be done in a day if the transmission shafts don't need to come apart to have gears/dogs replaced. His original problem sounds like a detent Spring broke or the detent wheel came loose somehow, it wouldn't shock me, it's only held in by a metal tab and bolt.
If it needs long wait time parts, I could be convinced to ride out after you get the parts in hand to assist later this winter.