Hi Art..!!
OK - taking out the sear spring can be somewhat daunting if you haven't done it before Especially true if your's hasn't been removed for a while!!! But - after the curses subside (and the blood stops flowing from where you have punched your hand with the small flat-bladed screw driver you used to lift/push the spring forward Ask me how I know!! )...
Then - remove the sear bar... You will see the surface that mates with the "lug" on the firing pin. If it's been "dressed" incorrectly, you'll see the mating surface may actually be "curved" slightly. Another trick I've seen is that the "lug" height has been shortened, so the engagement surface is incorrect... Make sense? It's tough to explain without a "Web Cam showing you live video"
As for replacing parts - you may find that you have to replace quite a few before you hit on a fix. The list of parts I can think of that need to be looked at include: trigger, sideplate, trigger lever, sear bar, sear spring, and firing pin.. YIKES!!!
Anyway - let us know what you find, OK?? And please post back if you need info on what you are looking at..!!
Best to you!
John D.