Hay G,
There is a simple fix that I use and it works. Go to your collection of brass tubing, and find brass tube that will just fit on the shaft of the wheel axle snugged. Try to get the tightest fit you can...a drop of CA will hold it in place if you clean all the surfaces. Then just cut the brass tubing to length, and drill out the wheel to fit nice, with as little side play as you can get away with. Then place a new wheel collar on the brass tubing...or drill out the old wheel collar. Most whell collars are brass and and use the same drill size you used on your wheel.

The wheels W.M. uses are cheap foam and will ware funny and in time cause you major problems. So is their fuel tanks.

Soft landings,
Bobby of Maui