If none of these methods works, you may have silicon smears. I had this on my travel trailer windows, and nothing would shift it. One day, here in England, my wife sidled up to a car windscreen repairer working in the street, fluttered her eyelashes at him, and asked how to get rid of the smears. He gave her a tiny pot of a reddish brown powder, which is, I believe, Jewellers' Rouge, the powder that jewellers use for polishing precious materials. It worked like magic on the smears. In the past it was used as a final polish by glassmakers. For those interested, it is a mixture of ferrous sulphate, ammonium hydroxide and ammonium water. This mixture is then filtered, and burnt in air. The residue is finely powdered, and this is jewellers rouge. You can buy cloths impregnated with it. A search on Google will show you where to buy the stuff, or try your local small jeweller's. If that fails, your local windshield fitter may have some. It's magic! Now would the guy have given me the powder? Nick.