Sort of post facto here but if considering the use of Coca-C for a rust killer, Don't. The recipe has been so buggered that the stuff can't even eat its way out of the aluminum cans anymore. I have consumed C-cola since I was old enough to have an allowance to spend on the stuff and the best was the pre-80 recipe. Once they went New Wave and Sugar free and Low Caffeine and got into all that customer appeaser cr*p the stuff went from wicked to bland and boring.
I have heard that industrial molasses like what is fed to farm animals is supposed to be good for rust removal. Apparently also happens to be eco-friendly. (Well, I guess you can't have everything, LOL).
Nick