I know everyone says to install the 3/8 or 5/16 ribbon tar like material on the windshield seal but the old guy that does all my glass work just told me not to use it because it will leak and dry out again.

He says he uses a dam kit and the urethane sealer and he has no trouble with trim fitments after wards.

I now have both seals I have tubes of the urethane plus I have the ribbon seals has anyone heard of this dam kit that goes around the inside of the glass and keeps the urethane in place?

My chevelle had the ribbon caulk from the factory and it was still sticking on everything when i took the glass out after 30 + years, i used new ribbon again when reinstalling my windsheild. Also there is a issue with the spacing between the flange and the glass, the ribbon gives you the perfect spacing and a urethane may be a little more difficult to acheive the same thing.

Glass needs to set the correct depth for the trim to fit. That will not happen using the tube stuff. If using the square seal use the 5/16, with the round use the 3/8 cause it will mash down to 5/16. The square will not mash down. Be sure to use the spacer blocks to center the windshield from the bottom.