I bought 3 bumper boy units used. 1 unit had 2 broken servos when I bought it. broken where the servos arms that screw down to unit attach to servo body. I replaced servos and have now had to replace 1 of the servos 2 more times for the same problem. Thats 3 busted servos while all the others have performed flawlessly. Does anybody know what I might be missing or what might be causing this?