Well, this is not helpful, but...
I called our local sailmaker, Kame Richards of Pineapple Sails. Well-known in the Bay Area. My main (Dacron) was looking a bit scrappy, so I asked his advice on cleaning the sail - light bleach, laundry detergent - what would he suggest?
Kame: "Buy a bigger hat"
Me: "Huh?"
Kame: "That way you won't see the stains"
He went on to explain that he does not recommend any chemical treatment to his sails....