Wires become old far sooner than motors, with time the impedance increase, and there is a voltage dropdown (check the present_voltage of each motor). Motors become under powered and they have not enough current for their torque.
Have you got timeouts ? For me it is related to the first issue.
If I change your question from motors to wires (as I suppose it is the issue), we could write a primitive which check voltage of every motors and suggest to the use to change older wires.