[itsnotanova]

This is my experience in the 13 Boxsters I've bought for my salvage yard.
1 I bought didn't come with the top
6 of them still had the original plastic window and all of the windows were either cracked or ripped.
4 of them had the window replaced and all of them you could tell from a mile away. Usually the stitching was off and looked like they were drunk when they were doing it. Not only was the stitching bad, but the thread they used fades quickly. Another problem with the replaced ones was the plastic would be slightly warped or wrinkled even when the top was fully stretched out. I will say that none of them leaked at least.
1 had the window replaced and it was done very professionally. Perfect stitching and the window looked clean and flat. The only problem was the thread they used faded, but because their stitching was so nice it didn't really matter. When I bought the car it came with receipts and I want to say they spent $400-500 to have it replaced.
1 had the complete canvas top replaced with an after market glass window top. I was able to track down the previous owner and he told me he paid $400-500 for the new canvas top off some Ebay company and then brought it down to the local upholstery shop and had it put on his frame for $200. The finished product looked great and the canvas looked and felt of good quality. From what I've seen, the after market glass windows are even smaller than the factory glass windows.