It looks like cola still works; they removed a key ingredient a few years back, phosphoric acid; those who drank a lot of coca cola risked having too much. This acid can be found in some rust removal products, but cola still contains lots of citric acids, ascorbic acid,... There's a lot of options for rust removaal, I lean towards finishing off with a suitable metal polish, most of us have one or two on a shelf some where. They bring back shine to the worn old bobbins. I can see my self sitting there holding a dremel with a polishing tip lol