Ed,
when you state that “the gears are shot”, have you removed the drive top cover to look? I am surprised that you got three years out of your loco as the plastic used suffers embrittlement, allowing the aft two top cover mount screws to detach from the drive block, allowing the motor pinion gear to separate from the gearbox drive. The aft two mount screws apply pressure on the aft end of the motor, keeping the pinion drive gear in contact with the other gears. If your gears are not stripped, then an easy fix is to obtain similar gauge screws, but about one inch long. Drill down the centre of the two aft screw holes with a small drill bit and then fit the longer screws. This will then allow the top cover to keep pressure on the motor and stop the drive pinion lifting away.