I have acquired a John Deere 403 rotary cutter. When I got it I was told the gear box was leaking. I assumed it was leaking out the bottom, but when my grandson brought it by I discovered the leak was from the plate that covers the back of the gear box. Further examination revealed the leak was a result of the clip that is supposed to hold the plate in place not being fully seated in the groove. I pulled the clip out thinking I would remove the cover plate to inspect the gears. I thought with the clip removed the cover would come out easily. It did not.
I could turn it, but not remove it. I tried turning it thinking there might be threads or a notch on the plate to match the notch on the housing, but was not successful in removing it.
Since I was fairly sure the cause of the leak was the loose clip I replaced the clip, refilled the gearbox with lube and used the cutter for 45 minutes. It didn't leak, was quiet, and ran cool.
It worked fine until I let it bottom out on a dirt mound today. I quickly raised the lift, but noticed that it sounded different. Then I noticed that the clip had come out. I was lucky to see it before it dropped off the cutter.
I thought no problem, I;ll put it back in and keep going.

I was unsuccessful getting the clip back in the groove. It won't snap back in and I can;t drive it back in.

Any idea what is going on here? How does one get the cover plate off when the clip is removed? Is there something keeping the cover plate from going far enough into the housing to let the clip fit into the groove? Any suggestions would be appreciated.