A cracked cocking piece is new to me. It looks like perhaps the S&W piece is cast, where as the original was machined. Anyway, what I do know is that once you remove the pins holding the cocking piece, they must be repressed into the frame. This will make everything tight again. That could of been your problem with the second cocking piece. You need a hardened steel piece that is shaped like a magazine that goes in the magazine well( I have only seen this tool once on ebay and wished I would of bought it) , and then press the pins from the outside with a vice. This will expand those pins in the holes. You may know this already, but I thought it important to cover it.
I am not saying a loose cocking piece necessarily caused the second one to crack, this is a myster to me, maybe there is a problem with the hammer, there is a little strut for double action that has a spring behind it that retracts past the cocking piece for single action that must work properly. As with most things it is hard to single out a cause. Perhaps Mike or someone else will have more insight than I do. You are definately getting into gunsmithing area here. I know of someone who works on ppks in the st louis area. If you are interested, send me a private message and I will give you his name.
