Holy Smoking Motor!

Get a hold of GGG or Gunrunner John on the forum if they can't help get a hold of Midge at MTH. 

If you take the motor out and measure flywheel dia, thickness, and worm gear length and threaded length I can match it up.  G

Frank Timko has done repair work/motor replacement,  where he removes the worm gear and flywheel and installs them on a replacement motor.  Most likely if one motor is at issue, the other motor is also damaged. IMO.

I think buying the MTH motor will be far cheaper than having the gear and flywheel removed and put on a new motor.  I'm pretty sure there will be a lot of similar locomotives with the same motor and gear.

As far as the other motor being damaged, I'd probably do a bench test on it with a DC supply to check it's condition.  I'm not sure why you think it is likely damaged, that's not been my experience.  I've never had both motors go bad at the same time.  In the rare instance that I have had to replace a can motor in a diesel or dual-motored steamer, it's only been one motor.

I'd just send the motor to GGG and he can match it up for sure.