This is a common phenomen in older trailers.
My conclusion is that it is "elastomeric strain crystallization." Some folks will opine that it is dessicant that has turned amber because it has reached saturation, but I did find an article supporting my theory that if you squeeze an elastomer between two panes of glass and then run it through 20 years of hot and cool cycles, the black rubber potting will extrude out into those funky amber crystals. I cited that article somewhere on these forums, but can't find it again.
Anyway, it may be weird looking, but it is non-threatening, and the only way to "fix" it is to rebuild your window. If you don't have any reason to rebuild the window (ie., fog or liquid between the panes), I would leave it alone.
good luck!
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