[Porsche9]

I've found that once the plastic bits are damaged and you use one of the various remedies that they are at best temporary in nature. The best is to protect from the start. Keeping the car out of the elements, especially direct sun exposure, as much as possible is important. In addition using a product that has some sort of UV protectorant helps. I've personally had good results using the appropriate 303 Aerospace Protectorant.