anybody remember KPS-14's and 20's. you had to clean the pot's after every flight.
Even some of the early JR's in ducted fans needed cleaning often.
check out the piece on JET SERVOS on TBM... they have tested servos and posted some results. http://www.troybuiltmodels.com/Servos.htm

another good piece of reading from TBM... http://www.troybuiltmodels.com/servo_testing.htm