I had same issue when reassembling my '40 windshield - problem was rubber weatherstrip from Jim Carter's - it was stiff, and impossible to thread into the " Tee " groove on the windshield frame. I bought new from Steeles Rubber and it slid in like a dream. You need to get it snug, and " weld " the butt joint of the rubber together. Steeles recommended a special adhesive which ended up looking like a Superglue type product. End result was a good fit, with a flexible leg which fits pretty tight against the body for a good seal. As for the glass install, I had an Auto glass shop install glass to frame sections with polyeurethane sealant - looks great / seals tight.
