OPTION #1: Do Nothing.

OPTION #2: Camouflage the defaced area with a Birchwood Casey touch-up
pen.

OPTION #3: Proceed with Hondo's recommendation (but don't stop at
removing the yoke and cylinder------strip the innards out
too).

You're going to make a mess with either #2 or #3. Start by
making the clean-up easy. Strip the innards. Blast the entire
area under the sideplate with Brake Clean and dry it thoroughly
with high pressure compressed air.

You're (almost??) certainly going to be flushing the new bluing
with water-------probably more than once. Get rid of the water
with air, then WD-40. Get rid of the WD-40 with Brake Clean,
and dry.

My two cents worth----enjoy and go with God!

Ralph Tremaine