Not sure it needs total dissembly and hole reaming.
I would just hose out the firing pin with Gun-Scrubber and blow it out real good with an air hose.
And I would
not cut the firing pin spring off two coils, because it will compromise drop safety to some degree.
After 10 years, it is already weakened considerably from use.
I think your problem has more to do with a weakened hammer spring in the grip from 10 years of use.
I'd call Kel-Tec and have them send you a couple.
1-800-515-9983.
Ask for Service, not parts.
"Parts" will sell you the springs & charge for shipping them.
"Service" will send them too you free.
Be careful when you put the new spring back in, as you have to reach down through the grip with a screwdriver and stretch the spring retainer cap back in place.
It is very easy to over-extend the spring and stretch it far enough to weaken the new spring putting it back in.
Here is a good read on doing it:
http://www.1bad69.com/keltec/disassembly.htm
rc