Unfortunate that you had to sell it. Our sympathy, of course.
But on the topic of surface rust and steel wool, I had an interesting (and new) experience with that issue last night.
I have a .38 top break that has excellent finish over most of it, but someone had polished several areas almost completely free of bluing using steel wool.
I thought I would try some cold-bluing on the bad areas, since it couldn't look any worse (I hoped).
It did look dull and blotchy after applying the cold blue, so I picked up a bronze bore-cleaning brush and started going over the blotchy area with that. It actually looked good after some brushing, and it took most of the blotching away. It may be that bronze wool would do the same, but if you happen not to have any, the brass brush may be an alternative.
I was planning to try some Flitz (or other) after that, but it looks good enough that I am going to quit while I am ahead.
It's not as shiny as the original, but for an 1880's firearm, it's not too bad looking.