6 yrs ago, I had a professional glass cleaning service to do my house, it was up for sale and the windows always had a film on them. He tried for several hours to do 8 windows and a bow window. with no luck in fact he refused payment. I have also tried all sorts of products to no avail, so I tried Gel Gloss, it's a fiberglass cleaner, Believe it or not, it cleaned the windows, I now use it to do the 2 glass shower stalls i have, works somewhat like Rain X water just runs off. In another instance I parked our Caddy under a tree in No Cal. whatever that tree sapped out and landed on the roof, hood etc, Tried WD40 to dissolve with some sucess but the Gell Gloss removed all the sticky residue and stains left on the paint(clear coat).I don't sell the stuff or have stock in the company, but I can assure you it saved my *** more than once