IIRC, it is anodized aluminum and black ABS that the switch's chasis is made from.
Anodized aluminum is "theoretically" fixable with a steady hand, a graphite cathode, and a solution of dilute sulfuric and boric acids--- but I would not recommend. (needs high voltages, needs a clean area to clamp the anode of your plating machine, etc.)
ABS could theoretically be fixable with a synthetic fiber based felt-pen, loaded with an appropriate solvent, like hexane. (USE WITH CARE)