Hi,

Can you move the control arm on the servo by hand or is it locked up? Does the servo make a noise but the arm doesn't move? Can you move the arm by hand but it seems to jump from resistance to no resistance. These are symptoms of damaged gears. In these cases undo the four screws that hold the sevo together and visually inspect the gears. If they are missing teeth or have bits jammed between the gears order/purchase replacements from the servo manufacturer and replace. If there is no movement/noise when connected up to the RX it could be as simple as a damaged connection or wire. If I repair these I always mark the now suspect servo and only use on throttle as nowdays the cost of replacing standard servos isn't as scary as it used to be.

WD40 which is mostly diesel is fine for cleaning the motor.

Cheers,

Colin