Following the advice on here. Polish up everything that you possibly polish up. I would then remove the main spring......can be done easily with a pipe cleaner by wrapping it around the spring at the tumbler end) I would polish and reassemble with out the main spring in to see how it functions. If it does not hold under moderate hand pressure at half and full **** then one of the internals is at fault and needs to be reexamined. I have two tc flint locks and using the methods from this forum have given me trouble free locks. as most say also check your sear lever clearence on the inside.