I tried to use lens cleaning tissue, but the mark just wouldn't go away. Ended up using more pressure, and scratched the print. I'm guessing some sort of solvent is required, I heard that lighter fluid, or 90%-100% pure alcohol (?) can be used. Can someone confirm this?
in my school darkroom we carry out the cleaning of negatives before printing with ronson / zippo fluid. I don't suppose it to have much effect on paper. you could try using photoflo in water to rinse your prints if you can afford the drying time. but make sure you dry it in a dust free or low dust place.