This must not be the right part, then, because you can see from my pictures above that the worm gear is on the axle. Either that or I'm missing something
Even if it's the wrong part I'll cross my fingers that the gear matches and I can swap it
Its really only the gear that matters. With the axles removable it should be fairly easy to pull the gear and wheels off. If possible use a press, even a drill press with a pin punch or hard steel rod. Don’t pound them off with a hammer or use a two jaw gear puller or you risk breaking the wheel flanges. 7 bucks is cheap gamble. Stock Drive Parts or other 3rd Party supplier will cost you 3 times as much and the gear still might not be perfect.