I'm not sure where vectorit is getting his info but the fixed vent window seals are VEHICLE specific and are a 1 piece seal not a 2 piece seal, I just removed the old ones on my 68 Suburban 4X4 and replaced them with new 1 piece fixed vent window seals made by Precision backed with a lifetime warranty.
We stock these seals and you'll find them on the following page of our web site
http://www.gmcpauls.com/Suburban_-_Panel.htm
Part# 1287374 $34.95pr
GMCPaul Jr