That front window seems to be a leaker, at least on mine it was. The passenger side mattress was always a little wet when it rained. The best I came up with (over 15 years ago) was to take a piece of thick Plexiglas and make my own. I then clear caulked it into place.
If I was to do it all over again, I think I would pull the whole dang thing out, then go to a glass shop and have one custom made reusing the frame. I did that on a 5'ver I owned and was surprised at the how cheap it was, and the quality of the work I got for that price.
Also you'll get a chance to reseal the thing proper when you install it.
