I get paid to do this, but you fellows get it for free !!!!!
1. Make a cleaning patch from an old pair of denim jeans or shorts.
2. Put a dab of flitz / maas cream metal polish on the rough side of the cloth & rub the hell out of the rusty spot---it will lift the rust off the metal, but will not harm the blued finish.
3. Do not let the polish dry---so flip over the patch & use the smooth side of the cloth to remove the blackened paste.
4. Use a clean patch & put a few drops of mothers / meguires liquid clean coat pure carnuba wax on the patch. Apply to the area, allow to dry to a haze, & buff off the haze with a soft flannel cotton towel.
You will get an eye-popping gloss to the blue surface & long-term protection from new rust & corrosion. You will be so blown away by how good that area looks, you'll end up doing the whole she-bang. Hint: Do the same inside the bore, scope tube, rings, bases, magazine box, spring, & follower.