Ahh, almost the same years here for me also. plus I worked at a chrysler plant that made windshields,side glass and backlight too! But I bet you scratched the heck out of the plastic ones by not unzipping and lowering it and the cloth in the zipper was probable dry rottet as all get out.. I work for a trimmer that does 60's Lincolns and every plastic window that comes in has a crease and scratched where it folds and rubs the well liner when not unzipped. the glass ones ...ahh not so much. though I do have to admit I used to never unzip mine till I realized how much it cost to replace one on a good top less than 4 years old. My take on it is if it's glass it can stay zipped, if it's plastic I'd unzip it just for scratch protection and creasing.Have had convertibles for forty years, I have never unzipped the window. Never broke one.