Just so everyone will know what the problem is, the large brass nut appeared to have started to work itself out. In turn, every time the carriage recoiled it was dragging on that brass nut. It finally got to the point that the carriage would not return to battery and just made a grinding noise unless I cut power to the tank. The nut is ruined so there is no saving it. Next time I will locktite that nut, which I think is actually the head of a brass screw if I remember correctly.