I wouldn't use brake cleaner, might melt the varnish on the windings. Use contact cleaner instead. Using emery cloth, fold it over so that you can do both contacts at once, while they are closed. This will help keep you from sanding in a high spot on one of the contacts. If they are especially nasty you can try a points file. Or replace the unit. As RR said, adjust the regulator while you are there.