Black Rigging Stains on sails!

Anyone have an idea of what the best/least expensive product to use for getting those ugly black stains you get from the mainsail rubbing against the shrouds while going down wind? tomorrow I'm going to use "Lime-away" on the sail. Next possibility is oxalic acid, which is also supposed to remove rust stains, then I've got some stuff used to etch aluminum before you paint it. I used to have some chemical used to remove the green stains left over from boatyards sanding down old bottom paint, and the wind blowing the dust all over your boat. Product #29 or sumthin. Jerry Sobel, Shpirtiz