There is a plug in the front of the gear case cover, a 3/8 ratchet and 3" long extension will remove it. It has a square slot that the the extension fits into, just like a socket. This will give you access to the nut on the gear, the gear goes nowhere, just sits inside the cover. When you put the pump back through the cover, take your fingers and push the gear up onto the shaft, then install the washer and nut. Use a magnet to to put onto the end of the shaft, then slide the nut and washer over the magnet, so you don't drop them in the gear case. You can do this on removal and replacement of the nut and washer. You shouldn't need to remove the drive belt. It does make it easier though.
When you go to reinstall the access plug, line up the start of threads on the plug to 12 o'clock, you can also turn it backward while trying to insert it. You will feel it straighten up, then turn it in with your fingers. All you need to do is snug it I mean like it is made of plastic, because it is. They will break!
Any troubles call me and I will help you.
Thanks, Shane