I'm sorry that I did not get a chance to take pictures last night, I will address ASAP.
As far as the cracking, I cannot tell you, as the screw/bolt tightens up against the door face to hold the vent window secure in this one connection point ... Once you have the screws, you could consider some Loctite blue or which ever is the one you can loosen up relatively easy. I think Loctite Red is the heavy duty one.
As you know, you have five attachment points 3 are on the door edge (two on the side and one on top), two on the door panel face ( one high, the long screw, and one low, the machine bolt.
LMC shows 4 of the 5 screws for sale, they do not show the one I think you are looking for. (#11, #12, #13) Maybe because their replacement windows do have that secure point, I don't know.
Explore our vent window components for Chevrolet Blazer, GMC Jimmy and Chevrolet/GMC Suburban 1973-91. Ideal for revamping and personalizing.
www.lmctruck.com
I had my original units rebuilt at a place in Oregon called Dr J's Restoration Rx The man I worked with name is Jerry and outstanding gentleman. He completely restored the units and look beautiful. It was expensive, more than LMC offers when they have them in stock.
The swing rivet on the base was broken and he restored mine to look brand new, painted, new gaskets, new locks, new spring, etc. Go to his web page and read about his restoration process.
I found out Precision Products rebuilds them as well but I went with Jerry after talking to him.
http://drjsrestorationrx.com/
Contact Precision regarding extruded and molded EPDM rubber, PVC and HDPE based plastics for the automotive industry.
www.prp.com
You can also check on this site to see if anyone has a set to sell ... I also bought a used set from a 1983 C-10 to have redone for another project at some time in the future.
I'll get back with the information.