I used all kinds of chemicals including bleach and 409,CLR, scrubbing bubbles and many others until i tried this Starbrite mildew stain remover. it really does an awesome job. I bought it at Academy sports but i think you can get it pretty much any major retailer. i waited about 10 minutes but it does not take that long, it only take a few minutes but i was busy taking care of other stuff in the garage and outside. Hope it helps.
Maybe someone can help me (sorry if this derails the thread): I have a 77 VW conv with a white top that the prev owner left under a cherry tree. The cherry buds left little brown stains on the top that are impervious to any cleaner. I've tried every cleaner there is along with various Internet concoctions like hydrogen peroxide + shampoo + Dawn. These bud stains are the strongest thing I've ever run across. Too bad since the top is in great condition otherwise. Feel free to PM me if you like. Try Starbrite Mildew Stain Remover. You spray it on and let it sit. It was designed for boats but it is THE VERY BEST stain remover that I have ever used. I used to have a sail boat. I sprayed Starbrite Mildew Stain Remover on everything . . . deck, hull, sail, sail covers, seat covers. Starbrite made them all look great. You can get it on your clothes and it won't hurt anything because it is not bleach. My boat is long gone (thank goodness) but I keep Starbrite Mildew Stain Remover around the house for projects that other cleaners won't touch.