I have a Sears garage door opener that's probably 18 years old. It has started acting up. Sometimes, when you press the button in the car or on the wall the door will start to open or close then shutdown. The lights will go off and the little light in the wall control will go off. If you gently tap the unit on the right side, side where the circuit board is, it will come back on and operate. I have searched for a broken wire or loose connection but found none. What do you suggest?