I have posted this before - we ran MTH Diesels on the 2-rail portion of the San Diego MRR Museum. I suppose my postings drift into the past.
We got three years out of the worm gears. That's the proper name for the bronze axle gear. Every third worm gear replacement required a new worm as well. MTH was very nice about supplying replacement gears. One unit needed axle bearings after about 15 years of continuous daily museum running, and they turned out to be Piper Cub aileron bushings, cut to length.
To remove an MTH worm ( again, proper nomenclature) I have two steel bars, machined almost exactly like gunrunner's puller. They get bolted solidly, the motor is suspended from them in a steel tube with a cushion in the bottom to catch the motor.
Then the worm is heated with a torch - hot, but not discolored, and definitely not red. The motor shaft is tapped with a tiny drift pin and a hammer; the motor drops onto the cushion, and a new worm is inserted with shaft Loctite. Never damaged a motor. In fact, those motors were indestructible - I don't remember replacing any.