Your risk is that "crinkley" might well be nylon instead of Dacron. Oxalic acid (or bleach) and nylon don't do at all well together.
Before you go to the acids, try a detergent to get most stains out. I use Tuf-Enuf which seems to do an especially good job on fabrics. I believe it has Sodium Silicate in it. Soak in your barrel (or a kids
pool) for several hours. They don't have to be submerged - just kept wet with the solution. Rinse well.
Next try a 1% bleach solution or an oxalic acid solution - but only for 1-2 hours. These hurt sail cloth so don't go overnight. Get it rinsed out. And don't use at all if the sails could be nylon.
Finally, acetone can work on stains where nothing else done. Wear gloves and eye protection. Dab and scrub with brush then rinse.