We recently featured the Tech Tip De-Yellowing Convertible Rear Plastic Windows by Jaye Koppenhaver in the February 2017 63/64 Cadillac Chapter Newsletter. I have uploaded it to our website and will link to this thread in from our Help Page.
Here is the link to the article: De-Yellowing Convertible Rear Plastic Windows
Excellent tech tip.
I wish I knew about this sooner. I decided to get a new rear plastic window because of the yellow and I saw some cracking. What I do now is before I put the top down which is a map folding science all its own is to unzip the window and lay it open in the trunk. I also with the new window began using some stuff I have used for years on my boat plastic side windows called Klear-To-Sea. It has a cost to it but it does do what the label says, namely anti-fog, anti finger print, anti-smudge, reduces glare, and semi repairs small not too deep scratches. I'm not pushing the product but it works on the boat where if the same stupid stuff happened in my car those people would be walking
The convertible top manual (previously posted on this site), suggests releasing the top from the front windshield locks to reduce strain before unzipping the rear window.