I'm cleaning up an old pair of Weinmann brake levers. Dissolved the remnants of the old liquified lever hoods with mineral spirits, but I'm not sure what do do--if anything-about the threaded plastic cable adjustment fittings that thread on where the (non-aero) cable emerges from the body of the brake lever. They're completely functional, but the part that was exposed to the light has a light chalky layer on it. The part that was not exposed to light is gray. Anyone know a good way to remove what I assume is a thin oxidation layer without damaging the plastic? I can leave them as is, but if there's a good way to clean them I'd kind of like to do it.