Something dripped from the ceiling of my office parking garage onto the front windshield of my X. It looked like a "mineral deposit." Washer fluid and torrential rain did not remove it. Some of it came off from the abrasive action of a cotton towel when I washed the truck this weekend. Then (maybe bad idea) I used some solvents on it and scrubbed some more. Even tried "goof off." There remains a residue. I don't think I've damaged the glass, but also wonder if this stuff (or my cleaning efforts) have damaged the coating on the glass. Griot's Garage catalog has a rubbing compound specially for use on "uncoated" glass. Is this safe? Any suggestions?