i just had one where once a week it would trip the 2p dashpot overload, this is the overload in the loop, vintage is a 21ucl 1961,checked everything oil, shuts, brake, put a megger on everything i could. what i found was carbon tracing on the big resistors on the top rear of the controller, they are the resistor's in the loop to feed your MG set, hit them with some compressed air and a rag(power off LOTO and test and verify)have not had a call back on that elevator in over a month.