Hi Bruce... If the adaptor is also aluminum, it may be powdercoated, but more likely enameled or anodized. I would try some Testor's gloss black enamel, like we used to use on model cars and such. Comes in very small square bottles. I've even had good luck with that kind of touch up using Sally Hansens Hard as Nails fingernail polish......Dan

...Might be easier to recoat the whole adaptor...