Probably worth a warm soap soak or maybe vinegar treatment to reduce any calcium build up in the head. Electrical-wise you could bypass the circuit to power the motor and see if it spins okay with either a variac or a variable dc power supply depending on what motor it is. If it still stalls then could check brushes/any gearing jammed up. If it doesn’t stall then I suspect a overcurrent or thermal protection circuit is triggering. Could be corrosion on the board, a heatsink coming loose, or simply a jam you can’t see. Lots of possibilities, but people who work specifically on these would know more about the most likely things.