I think it's fixed. Cleaned it with the side plate off. Insides were not very dirty, nothing bent or seemingly worn, other than a little shine on the cylinder lock. Then, with a strong light, spotted a bit of (shock) corrosion along the side and top edges of the slot for the hand. Got out the sharp picks, scraped off a bit of hard brown crud, cleaned with a stripped down q-tip and CLP. Loaded up the snap caps and dry fired 60 times - not one hesitation and hang up.

So it was dirty, but not in the usual way. The tiny slot is so narrow that many of us don't usually do more than a cursory pass with the edges of a oiled or solvent soaked cleaning patch.

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Heavily armed old man.