Both posters gave great advice. The re-passivation happens very quickly. In your particular case, I doubt the SS is rusting but iron that was embedding in the SS with the tool. When I built my stand, I was in a hurry and the grinder had a regular wire wheel in it, not a SS wheel. The areas of my stand that I hit with the wire wheel are all rusting from the metal I embedded in the SS.
I need to go back and hit them again with the SS wheel. What was it my dad told me when I was a kid? "Never enough time to do it right but always enough time to do it over"