My gunsmith identified the problem as being a "worn hammer". It appeared to him that some previous owner filed down some internal parts, probably hoping to make the gun's trigger lighter. Apparently, he took too much off the hammer. Since it is a matching number piece, I had him repair the hammer by welding a bit of material, and reshaping that area. It functions properly now, as does the safety (which always gave me problems). The pistol will now go to auction, as a "new" trigger would decrease the value. It still needs to be re-bored to be a good shooter. Interestingly, The original grips are 50 numbers off from the gun; 171 rather than 121. Maybe someone back then had poor eyesight?