George,
You might want to get into the breech mechanism a bit, to see if either crud is keeping the left firing pin from moving freely, or if the spring that drives it (a pretty stout coil spring) is broken badly enough to reduce the force it is generating.
Just soaking the entire breech can work wonders. I have hosed everything down on a dismounted sliding breech with Break Free (or, automatic transmission fluid) and allowed it to sit, upside down on a rag for a week or so, and then soaked it in mineral spirits or diesel fuel, blowing it off and lightly re-lubricating, on guns that weren't too gummed up. 9 out of 10 times, it is all they need.
The firing pin spring is contained around the firing pin, and the guns usually continue to work, even if they are broken in one or two spots. But, there is going to be a limit on how many breaks in the spring the gun will tolerate before it no longer works reliably.
Best,
Ted
