If the rust is not penetrating (coming off), it sounds like your barrels were not clean enough (oil free) prior to your rusting process.....after your 320 or etching process did you clean real good with acetone and dry before the boiling--the type of carb cleaner could also be a problem, some leave a residue.....?.....I always clean with acetone......which removes any and all oil.......could also be weeping impurities out the weep holes in the bottom rib...?...Bottom line is 'clean and etched' is the problem if the rust blue/brown is wiping off with oil....IMO.......
Best of Luck.....
