[Dwight Southerland]

Go to building supply store and look for silver colored silicon in a caulking tube that says it is for sealing aluminum windows. Be sure the area you want to seal is very clean - use laquer thinner, brake parts cleaner, etc.; the surfaces should be sqeaky clean. Apply the silicon sparingly and forced into the gap between the wheel halves. Too much silicon will add to the mass of the material and can be forced out by the inertial forces of the wheel spinning at high rpm.

That's the procedure I have always found to work.