Jeff,

You have to get rid of the oxidized surface of the pop-top first.

A buffer, and some 3M heavy duty liquid rubbing compound will do this
job fast.

Then go to a Marine supplier (I know Boat US has this) and pick up a
quart of Penetrol.
It is a liquid, and you rub it into the fiberglass, with a rag, and it
restores the UV damaged gelcoat.

I did this to an older glass boat for one of my customers years ago, and
it lasted a whole boating season.

Then all he had to do was apply the Penetrol once a season, to keep the
hull looking good.

Have Fun,

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Terry--
74 Campmobile- (Clementine)
85 GL- (Delilah)
86 BMW 325 ES- (Eva)