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.
