I parked my boat in the driveway of our new house. A birch tree adjacent to the driveway has dropped sap and leaves all over the boat. I pressure washed most of the sap off (from a distance of about 4 inches), however the leaves have left brown stains that the pressure washer and Simple Green would not remove. Has anyone ever experienced similar problems with this type of staining and if so what are the recommended removal techniques. Thanks, Ben.