1988 chevy stepside 4x4

i need to know how the rear slideing glass comes out of this truck theres no rubber seal around the window that i can find on it. my dads 1998 trucks the same and we both need to replace both windows

They are glued in you have to cut them out...

I broke the one in mine and smashed out all the glass and use vise-grips to pull out the channel then used a chisel to clean it up..I let the junk yard cut out the replacement,it was worth the extra doh..