Get you to a hobby shop, and buy a tiny jar of Testor's Gold ( or Silver or White, etc) Enamel model paint ($2 ?).
Use some lacquer thinner to clean the lettering of oils (let it dry a few mins), flood the lettering, etc, with some of the paint and let it dry a few minutes.
Put your finger in the corner of a clean rag, dampen it in either clean lacquer thinner or mineral spirits, and LIGHTLY wipe the gold paint from the receiver or barrel surface only.
Don't press/rub too hard, or you'll drag the paint out of the lettering.
Once the bulk of the paint is removed, let it dry at least a half-hour and go over the surface again to remove any holidays.
It's OK to oil the surrounding steel the next day, but I would never oil the gold lettering.
Try not to let cleaning solvents on the area in the future, but if it gets blotched, touchup is a snap.
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