Get a sealable gallon container and put a quart of automatic transmission fluid and a quart of acetone in it then dump that gun in it and forget about it for a month or two. When you pull it out, you should be able to wipe off the rust with a cloth or some bronze wool. Don't have it refinished unless you are willing to eat the cost. It won't make the gun more valuable.

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Guy
SWHF #474 SWCA LM#2629