I have the same problem with my 1995 Four Winds. It is not the seal between the fiberglass and the window itself, it is the rubber gasket around the outside of the window like on a windshield of an old car. Mine has also pulled away from all four corners. I don't think it is leaking but am planning to take it to a shop that replaces auto glass unless someone knows where to get it and how easy it is to replace.
http://www.all-rite.com/index.php
Here is where I got my window glazing from, I sent them a small piece of mine and the matched it up. Cost me $1.14/ft
JKaz
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