I have very little experience with Browning salt guns, but recently bought a mint looking 1968 12 gauge 28" modified and full round knob Super at an internet auction. The price was such that I didn't care whether it was a salt gun or not. There was a thin line of missing blue on one side of the action against the stock, about an inch long and as wide as a line made with a ball point pen. On removing the stock, I found that the inside of the action was unblemished, no sign of rust at all. The gun may have been a salt gun, but no evidence of it. I am not a fan of short tang Supers, but couldn't pass this one up.
