If the part ur trying to remove rust is removeable, use that acid, which is locally called namak ka tezab (Salt acid) for cleaning newly done tile flooring and radiator servicing.
I learned when i had to get a air cleaner cover side clip made by a bumper repair guy and he used a thick iron sheet which has some surface rust so i told him no i want it to look like the other original clip (clean).He dipped it in tht acid n wow, it was a shining metal, no rust!
I dont know if for non removeable parts it can be sprayed or something or how it is to skin or how dangerous its fumes wud b...But in a water spray bottle, this acid does wonders to remove surface rust n costs damn cheap.
