Mixed Success
I agree with Dave about having your sails inspected and cleaned if they are still serviceable or can be made so. But why not try this innocuous solution first. I have removed some gundge using Ivory soap flakesl, warm water and a scrub brush. Lay the sails out on the lawn. However, you have mentioned the 2 hardest stains to remove from Dacron. I have had some limited success using a "mild" synthetic stain remover. Be careful though and try it in a small test patch. You do not want to weaken the fabric by using anything that will attack the fabric. If it was me I'd try the home remedy first and migrate to a sail cleaning service if you don't like your results. Good luck. Don
