You said above that you don't have to losen the nut to swap cases. The PTO gear sits inside the seal, which is all held on by the nut. If you are swapping cases, you should replace the seal, which would involve removing the nut to remove the water pump gear and remove the PTO gear and key, then the seal. In your first reply you say no you don't have to remove the nut to swap cases, which is WRONG. Duh.