God news for me: I wrote above about misfires. I was getting almost 30% misfires using CCI, Aguila, Norma and Federal ammo. Brand didn't matter. The firing pin (i.e. the hammer nose) looked fine, absolutely unworn. So the problem was a weak hammer spring. Replacements aren't available, so the fix was to slide a couple of washers between the top of the strut and the spring. Misfires are reduced to something like 2%, which I consider acceptable for a long out of print plinker. (A better fix would have been to put the washers under the spring, but this proved impossible.)