Dacron is more difficult. It's essentially a polyester fabric - which isn't great on it's own against a lot of solvents (it is listed as "marginal" resistance against MEK and Acetone...which isn't great). Dacron sail cloth also has several different coatings and binders that might also be affected by solvents. By the book, there probably isn't an easy way to remove the paint from Dacron without some risk of damage to the cloth but maybe someone else has some more practical experience.