Made an interesting discovery today: MTH bump-and-go trolleys and K-Line speeders/hand cars use the exact same motor! So, if you have an MTH car with a burned out motor, and a donor K-line speeder/handcar, you can swap the one from the other! You'll have to swap worm gears and shorten the shaft on the K-Line motor, but otherwise, it should work just fine!
Mitch