Robert-
This is a great tip, and extremely helpful when the doors bind and cannot move without considerable effort.
Another item to check are the microswitches next to the motor-gearbox; each assembly has a pair of switches that regulate both motor power and rotation. If the switches are out of alignment the door motors will make a loud buzzing sound until power is cut to the motor. To correct this open (or close) the subway doors, loosen the two screws that hold the switch bracket, then slide the switch forward (or backward) until the metal travel slide engages the switch actuator and closes the switch (signaled by a click sound). The switch actuator can also be bent slightly to ensure the switch closes at the right point.
I enhanced your image and added labels to the relevant components to check; once the switches are adjusted properly the motor will promptly turn off when the doors are fully opened or closed.
-John
