How to repair/waterproof Arch Top Windows
That looks like it's the seal between the two panes of glass in a thermal pane window.  If that's the case, then the main concern would be getting moisture in between the panes that would cloud the glass.
There is no repair for a seal like that that I know of.  A glass shop may be able to make you a new thermal pane insert that fits into the frame.  Or try to contact the window manufacturer.
Note that my daughter has had windows like that in her house for almost 10 years now.  They have not clouded up and there is no evidence of moisture between the pans of glass.  And no indication of any other sort of leaks.