+1 on the Rain-X. I have always been a fan of it's properties. That said, however, beware a new Rain-x product called Swipe-n-wipe.
If this is on a glass windshield use a COPPER wool or wire pad. Copper is softer than glass. Do not do this with a steel wool or wire pad. Despite rumors to the contrary steel is harder than glass and can scratch it. The copper pad should cut through anything right down to the glass. If you used the swipe and wipe on a plexi windscreen you may be hosed however.