I know this would be harder than trying to do a handgun, but I am a firm believer that if the steel parts are degreased, and then Boiled in "distilled water", then the rust that is there will be turned to Bluing, and will not leave as much differance in the finish.
It will probably be a discolored spot, but at least you will not have the existing Bluing thinned out by the polishing around the flecking.
It all goes back to the same process used in Slow Rust Bluing.
But the Degreasing, Boiling ,and then Oil Curing will Stop the Active Rust without abrasive wearing of the existing Bluing.
Polishing will remove the rust or Flecking, but there is Bare matal at the bottom of the flecking.
The conversion of the flecking by Boiling in Distilled water will give the bottom of the deep flecking a coat of Black Oxcide, that is basicly Rust Bluing.