I bought a Pearson Ensign once and the engine had been sitting on top of the sails all winter. The engine gas and oil mix had soaked through the main and jib to create a tie died effect about 3 feet round. I went to Boat US and purchased a product I think was simply called "Sail Cleaner" (sorry I don't remember the manufacture). It was a small container of a powder that was similar to Oxy clean that you would mix with water. My next door neighbor, and my wife watched as I wet the sails and applied the cleaner then we all stood back thinking this was completely futile. Per the directions you had to let it sit for a few minuets. We all stood there in shock as the stains completely disappeared not to mention that the seams and the rest of the sail went back to a nice clean white. I had that boat and sails for four years (before I found my way to an M-17) and the sails held up great and never showed any signs of damage from the cleaning. I passed the rest of the cleaner to a friend to try and get rubber scuffing off of his sail but it would not get them out though the rest of the sail looked great. My friend did not return the cleaner and that's why I can't remember the name, sorry. Try checking with Boat US, I went to there web site but didn't see it there. Good luck, Briant