All the books I''ve read & sailmakers I''ve spoken with suggest using a mild dishwashing detergent, like Dove or Palmolive. With a soft brush, this gets most of the grime and some of the other stuff. Sunlight should put the mildew and mold on hold. Leave the sail out in a flat spot on a sunny day and turn it over a few times. The big oil spot a previous owner left on one mainsail was not affected by this procedure, so we have been tempted to try something more powerful. Bleach or other chemical cleaners may cause the plastic (even dacron is plastic) to deteriorate, however, and we think a big spot is better than a big hole. We are therefore waiting until the miracle cleaner turns up before attacking the oil spot(s). What does your sailmaker suggest?