I have firsthand experience.
My 1998 986 Base was purchased at a local P Dealer in 2011 with 23k on the clock with a new engine replaced by them in 2006 with 20k. The car came with a hard top and was used like that for many years. When inspecting the car, the convertible appeared that it was never used and still contained plastic factory wrap. The mechanism had problems closing and of course was a condition of sale to repair.
The performed some cable adjustments, but the roof would still not close. The problem was that the cloth had become stiff and taut being tucked away for years. Dealer saturated the fabric with a soapy substance, got it closed, and let it sit in the sun wet for a day. Roof was perfect at delivery. The plastic window was perfect as it was protected for years by a waxy form shaped protector from the factory.
I found Porsche part
98656385501 from Suncoast. I use it every time the top is down and my plastic window is perfect. It's a pain and all with the "Boxster Chop", but if I'm out of the car I don't mind the extra effort to grab it from the trunk. Plexus used often to keep the window supple. Car is a garage queen, so I'd like to keep it nice.