Most of the vendors that offer replacement rubber for these trucks procure the stuff from Chinese repop manufacturers. The window channels seem to work OK, however the vent window rubber and windshield rubber is way too big. The only way to make the windshield rubber work is to cut it in two and remove approximately 4 inches, placing the joint at the bottom center. When I restored my M1028, I did not want a joint which could possibly leak, so I searched online and found a new OEM old-stock rubber from an obsolete parts vendor. This GM windshiled rubber fit perfectly. Regarding the vent windows, I fooled around with trying to replace the rubber for about a week, and finally threw the things in the dumpster. I wound up purchasing new GM OEM vent window assemblies from one of the obsolete parts vendors which specialize in such parts. I believe I posted these GM part numbers soewhere in my rebuild thread.
Hope this helps.
