It sounds like your friend the gunsmith may have taken too much material off the sear notch on the hammer in a effort to lighten or smooth the trigger pull. I believe you need a new hammer and I would opt for a Chip McCormick hammer and trigger group (hammer, trigger, sear, sear spring). You can also just get a standard 1911 style mil-spec hammer from any of the major parts houses like Numrich Arms, Brownells, etc.