I have a black handle super adjustable that was extremely rusted, gunked, you name it - stuck, wouldn't even open. So I squirted it with some liquid wrench-type solvent, which got rid of the rust and, after a while, loosed the tto mechanism up great. Scrubbed it off with Scrubbing Bubbles and soap, and it cleaned up just fine. But now I've noticed a little white residue on the black handle of the razor that I don't think was there before and that I can't quite remove. Any ideas on how to clean the black handle of these adjustables?