I used Duragloss 501 on my 1987 fiberglass boat. While I like it on my Jeep, I am not sure its doing a good job on the gelcoat. The hull is white with a gray section about 6" wide about 3' above the water line. The white sections look OK, but the gray looks weathered. Its smooth as glass to the touch. Also there are some stain lines from the cockpit drains and the Duragloss 501 is not really doing much on the stain lines, even with some rubbing. Any suggestions?