Replace it. I have a bunch of them broken in a dorm building I take care of. What usually happens is people try to crank it open when the lock is on or they try to close it then the lock is on and it bends metal inside the crank. Have had no luck repairing them.

there should be little pressure fitted caps that you tap onto the axle to hold the wheel on

When I saw the Emperor's palace in Japan they let me crawl under and look at the floor joists.

I hope your comment was meant as a joke.