The windows were really bad. I'm sure when my back window was slashed, they just unzipped it and replaced it. I then got it in the habit of half folding the roof, hopping out of the car, creasing the window in the middle and then continue with the folding. Eventually it would just fold in the middle - that way I only had one crease. I traded it 5 years ago on a 156 wagon. we now have a 159 wagon (to go with my old 164Q)

I used to own a 98 spider with the exact same problem. I tried cleaning it with special plastic scratch remover and it helped about 50% better and lasted too. I did eventually replace it though when it was slashed but opted to go for the $500 option as it was better quality plastic (Thicker and more scratch resistant) as I knew a guy who changed his for $300 but after putting the roof up and down a few times it would actually stay really creased for a long period of time. Id first try the plastic cleaner as it is only worth $20 and is the cheapest option.