I think I've isolated it to the spur on the plunger rocker. Compared to the reference pistol, and an understanding how the trigger sear works, if the plunger is too long, the sear can't rest on its designed rests, bringing it too far away for a worn sear to lift. If I file down the plunger spur, and replace the lock stop to reduce play, I should end up with a functioning C96, if out of spec.