I've got a legacy Big Boy #4012 (6-11126) and it recently developed a problem with the gearbox on the rear set of drive wheels. The rear gearbox is loose and jumps up and down as the engine runs. The gear box is held down to the chassis by a screw with a spring. I've retightened the mounting screw and the gearbox still moves around a little. Also the plate the covers the exposed gears has come loose and when I try to put it back on the screws don't grip the threads and the plate falls off. I've included a video to show the gear box wobbling around.
Any help on this repair is greatly appreciated.