The Servo's gears could be stripped. But, so could the spline in the servo arm itself. Also, if you are stripping servo mounting screws in wood mounts, you can harden the servo screw hole in the wood with thin ca.Thread the screw in, take the screw out, add a drop of two of thin CA, let the CA harden, reinstall the screws. If the hole is already stripped, do the same with medium CA or shove in a tiny piece of wood and then glue it in. Re-drill the hole and go from there.