Andrew, you answered a couple of other questions I had at the back of my mind. I have had the same issue with re-striking the same case still in the gun, and you are right, no matter how many times you hit it, it still won't go off....but turn it 90 degrees and it does. I can't explain it either, just does. I have the same issue with primers, just seem to catch as they go in, but they seem to go off. There seems to be no rhyme or reason why the light strikes happen, I had PK take a look at mine (mid competition last year) and he tells me that it looks like my hammer is falling off the sear at an angle, so falling early (so another theory).
I think I can force mine to light strike by not pulling back straight through, just one of my theories to make me squeeze that trigger. My hammer still has the spur and the original spring in it, it really doesn't matter if it is heavy, just has to be smooth. I have a little Mod 10 with no sights and a 4 inch barrel, totally stock standard but can shoot 480 with it in WA480.
Wind the spring up, look at those sights, squeeze that trigger and most of all....believe. I don't think it has anything to do with the firing pin spring, unless someone here can convince us otherwise.
You think 3+ months is bad, I won't tell you how long PK's list is. The big Q dropped my gunbox going up to Cairns last year and bent my Aristocrat, PK took it home and fixed it that arvo. When I asked him about building a gun for me as I already had one in the safe ready to go, he told me to leave it with him and see him next year to see how it's going
.... it's still in the safe.