I believe that molded plastic stuff is actually hardened setting tape. It gets very brittle with age. But if it's not original glass, it may indeed be some sort of molded plastic.

Have you tried asking at an automotive glass shop?


Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.