There is only one of two ways to repair a crack in a vinyl window. The first, if your canvas is still good then consider just replacing the vinyl. Many people don't realize that a marine fabricator can come in and do this without replacing the entire panel.
The second way is to use a an adhesive patch such as tear aid. The down side of this, is that it is a patch and it is also opaque and not entirely clear like the vinyl. This works though and if you don't mind seeing it, is the quickest way to deal with it.
On the down side, usually when a vinyl panel cracks, it is getting old and loosing flexibility. The other reason they crack is extreme cold. Folks will pull them out of storage on a chilly day, where they have been creased up and try to open them. This is when they are most inclined to crack. Storage should be done very carefully and with thought. You can find more on that on my boat enclosure page. Hope this helps, at least two solutions you might try.
Happy turkey day, gobble gobble!
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