I'd try and flush it out with one of the spray cleaning/lubes and see what happens...
If this doesn't solve the problem I'd get a new spring. Like I said they are very easy to replace... and believe me if anyone can screw up a gun or have a spring shoot out into never land, I can do it.
I shot my KP95 with the new 18lb Wolf Spring last week and it worked fine through 30 rounds.
I think the only other possibility is the firing pin has worn down and that will probably be a smith job... I'd leave that as the very last option.