I have an H&R 999 that works good except for a couple of problems. The barrel latch on the top of the revolver works loose after firing a couple of rounds and has to be pushed back into place each time. The second problem is that the cylinder comes off the shaft when extracting empty rounds. I push it back on the shaft, turn it, and it locks back into position. I'm sure these problems are due to a couple of worn parts. Has anybody ever had these problems and which parts are needed to fix them?