I  am new to this forum and am hoping you can help. I have a 3F loco. The loco wont run, the wheels wont turn either by motor or pushing along. The wheels just stop. By dismantling the motor the wheels and gears run smoothly. Similarly with the wormdrive disconnected from the gears, the motor also turns smoothly. As soon as all reconnected, nothing. The wormdrive appears to engage in the gears. Please help