I have a 1984 Grady that also has dull, chalky gelcoat that I can't get a shine out of. I was watching a boating show on TV when they tried a poly product on an old faded boat finish, and it looked like new. I copied the sites' webpage, and intend on trying their product before doing an expensive painting or new gelcoating job.
Check link below to see their product. Down the page on the left is a video of a sample boat they did. Looks good, but who knows?
Let me make this clear, I have not at this time used this product, nor do I have anything to do with this company. I just think it may turn out to be a good alternative for people like me that have an older boat with faded gelcoat. Mike
https://secure2.securewebexchange.com/poliglow-int.com/order.phtml