Plastics are failing the test of time... In museums, the problem is becoming more apparent, Dr. Rayner said in an interview: Plastics are reaching the end of their lifetimes kind of now. Of all materials, plastics are proving to be one of the most challenging for conservators. I find plastics very frustrating, said Mr. Collum. Because of the materials unpredictability and the huge variation in forms of deterioration, he said, its just a completely different world. We have a very short history, in comparison to other materials, in understanding how long those materials last, said Hugh Shockey, lead conservator at the Saint Louis Art Museum. Metal, stone, ceramic and paper have survived thousands of years, while plastics have existed for a little over 150 years.
The whole article is a very good read - about how art and cultural historians are trying to find coping mechanisms for challenges we toy collectors recognize, like photodegradation, plasticizer leakage, and just crumbling to dust.
They also note that dusting plastics can cause damage, so a compressed air can is the better route (museums use clouds of liquid nitrogen vapor to "cling" to dust particles and carry them away).