DH and I were cleaning out old paint, etc stored in our walk-in space under the house. Had some Thompson's Water Seal can that had developed rust on the bottom and some of it leaked out on the flagstone walkway. I immediately hosed it off but it left a water-repellant surface on the stone. What's the best way to clean this? Or will it just eventually wear off? I don't want to waste a lot of time and effort on something that won't work. It's not a huge area and isn't terribly noticeable.