Youi said this is used equipment. Servos as they get older will tend to hunt under vibration. In fact brand new servos will sometimes hunt under vibration. Are your ailerons static balanced? It would help if they are.
Hunting is a characteristic of low deadband strong servos. You may not see it but its there. JR servos have been set up with zero deadband. That means they will always hunt.
If I were you I would go ahead and fly it. You dont really have a problem.