Have you tried equal parts dawn and HOT white vinegar. I use this on tubs and showers to remove scum. Spray on, let sit about 30", and wipe away. Use a magic eraser if necessary.Rinse with a moist sponge. I use this same mixture for floors, drive tops, etc. My husband even asks me to make him a bottle to clean his boat after a day of deep sea fishing. A spray bottle full of vinegar with 4-5 drops dawn works great on windows, too.