Fixing or replacing Alfa Spyder roof

In the old days it was common practice to use saddle soap and warm water to protect sports car roofs, so you could try that. You could also try using one of the trim rejuvenator products for sold at most auto stores and there are polishes available that claim they will clean up the rear window. If the window is badly fogged it's probably best to have it replaced, and a motor trimmer can do that for you.