Similar things happen on my old Mantua 4-6-2, it's a pain, but I love the locomotive anyway. I claean, make sure the rods are in good order, and lubercate all the moving parts, motor and superfical. Mantua's are nice, but all look the same per type... Except the Petticoat Junction Set, that's distinctive! Live with them, love them, and take care of them as best you can.