To those who may not be aware, there is Z3 part (small soft cotton cloth with clips) that go over the rear convertible window to fully prevent those lines in the plastic, as well as scratches. It is $10 part that may need to be special ordered. I had one ordered and it works perfectly on the Z8. It took one day to get. The part number is 82-11-1-469-778, it is described as 'Z3 RR Window Cover. With my BMW CCA discount it cost $9.45 including sales tax. The cloth is a dark beige or khaki with Black 'BMW' letters in the middle and black borders all around. Works perfectly if you are like me and prefer to mostly keep the top down. Eliminates worries about the plastic window.