We have a 22 year old house and 2yr ago replaced the shower doors in two bathrooms with new glass doors. The point is, my wife tried everything to remove the scum on those fiberglass enclosures, and nothing worked. As a last resort, (without telling me, as I would not have let her do it) she used SOS pads with lots of soap. They turned out beautiful, no scratches, and 2yrs later still look good! I think the trick was to go lightly and use lots of dishwash soap as a lubricant. Good Luck!