Most operators just cut a plastic washer from a butter tub lid or something similar. Cut it round to about 3/8 to 1/2 inch. Drill a hole in the center slightly larger than the axle. Then cut a v notch so you can slip it over the axel, between the wheel and the frame. Problem solved. You may need to put two on one axel, till it runs smooth. I have done this on a few engines. As far as I'm concerned it has been a permanent repair.
Chris