In my "admittedly limited" experience, the presence of red rust means the blueing is already corrupted.I have used mothers aluminum and mag polish to remove some level of corrosion. There is another brand in a toothpaste tube sold by fancy kitchen stores that seems to have a less aggressive grit in the paste.
Agree with greying too. Polishing is mechanical. But Fe+O>FeO is only reversible under conditions which don't support breathing.
Polishing compounds are just cutting grains immersed in a lubricant. (You can polish plastic headlights with toothpaste to De-cloud) so realistically you could mix a little baking soda in liquid wax and slowly polish away corrosion.
You could always buy some junk at a gun show and try different things.
I figured the above on a garage sale scope with good optics and ugly scabs.
