The same motor by Mabuchi is used in the older Aristo 0-4-0, the Hartland Mack and the Bachmann 4-6-0.
Mabuchi RS-385PH. It is on the Mabuchi website but the stock motor does not have a long shaft so no use as a replacement. They were made to slightly different specs and shaft length for different manufacturers.
The Hartland Mack engine is almost the same wheelbase (a few mm wider) and has the same brass worm gears as the older Aristo 0-4-0. The worms are long enough so the slight wheelbase difference may not be a problem but the worms could be pressed closer anyway. You may have to shorten the shaft ends a little for it to fit into the Aristo 0-4-0.
Hartland may be your best bet for the replacement motor.