To add more specifics. Bought vent window rubber for my son's 66 GMC from"Sisters". We fought it for hours getting it in and finally got it back on and it took vice gripss to hold it closed to latch it. Not useable.
Bought Steele rubber for the same window-softer pliable easy to install and WORKED! Worth the difference in money because one just wasn't right and Steele was.