Penny, my first thought is to have a word with your nearest friendly Laboratory technician and see if they will let you have a small amount of Phosphoric acid which is real neat and removing rust without attacking the underlying metal, much gentler than Hydrochloric etc, It may need a little time in contact with the stain so if it is in an akward place, like a vertical surface for instance, wet a paper towel with the phosphoric and it should stick long enough to do the job!! wear gloves!!and goggles when applying it , splashes are NOT pleasent