I have on occasion repaired window, hatch and similar gaskets by squirting RTV silicone into the damaged spot. . . . . .covering with Saran Wrap, then closing the window.
When the silicone has cured, open the window, the saran wrap will pull right off, and wa la you have a repaired gasket.
Trim with razor blade if needed to remove tails or overflow.
And remember RTV, stands for Room Temperature Vulcanizing, takes forever to cure in cold temps.