Hey guys awesome forum! I picked up a new to me 2002 Boxster s triple black in like new shape.  It has 30,500 miles. The car was mint when I bought it Oct 1st.  I had the top down for about a wk in my garage and didn't think much of it, today I put the top up and see a big wear line across the rear plastic window.  I wanted to cry! The window was perfectly clear when I bought it now its all screwed up. It does not appear I can fix without replacement but should this have happened? I assume it is damaged from where it folds up but it hasn't been that cold.  The lowest it has been was about 50 F.  
So anyway can I replace it with glass or does it have to be plastic? Also can I get a tinted piece for it?   
Btw I love the car and only wish I bought it sooner!