I’ve never used it on a windshield before, but Seal All (available at auto parts stores) does a brilliant job if you’re not trying to fill a big gap. It is clear & not as messy as Sikaflex. I sealed the toe rails on my 28’ sailboat with the stuff. Almost invisible & was still watertight after 5 years. if you have gaps to fill, Sikaflex or 3M 5200. I like the fast cure 5200, personally.
Use masking tape along both sides of the damaged seal with a big enough gap between to expose the damaged area. Squeeze a small amount between the tapes. Smooth it out with a T spoon and remove the tape before it hardens.
Keep lots of paper towels on hand & toss them often. Vinyl gloves is a good idea too!