I have just rebuilt or replaced both drive motors. The left was rebuilt I bought a new one for right. The right was not turning so I replaced it and mechanic said the other needed repair. So I did. When I got it back both worked now the right has slowly stopped working again. I bought the motor not the mechanic. Is there anything else that could cause the motor not to drive. It seems like it will bog down but not turn. I have heard there is some kind of drain back valve that can get stopped up. Any ideas. Thanks Joe Bohannon