I have a 1972 Starcraft 16' runabout. If you are standing in the boat looking out the back at the transom, there is a small section 6" or so of exposed plywood. This section is weathered by the sun. I put some exterior paint on it to seal it. Do not know if it really helped much. The transom is solid and I want to keep it that way. What can I seal this wood with? Do I have to sand off the paint befor I seal it?