Is the wheel coated with clear "something" already that has gone "blotchy"?? If so, the existing clear has to go....remove it with the strongest gel-type paint stripper you can get. Once you're down to bare aluminum, use fine or extra fine steel wool and solvent to get rid of the corroded spots and bring up a nice shine on the machined surfaces. For the REALLY corroded spots you can use 400 grit emery cloth and then finish with the steel wool. You can also use commercial polishes to do the same job but some of them are quite expensive. If there are "as cast" rough surface sections of the rim, that's a whole 'nother story. Those sections need a wire brush or plastic bead blasting which will (usually) take off the clear at the same time. Consult your local plastic bead blaster for details. Gareth is right about the hub...otherwise if the clear seems OK (non blotchy), clean it up with Turtle Wax or some other wax with a mild abrasive in it. To respray your clear, use a clear plastic enamel NOT a cellulose based laquer as laquers have a tendency to yellow with age and weathering in my experience. Good luck.