Paint problems of the 2004 Lexus GX

The paint on the plastic fenders, bumpers, and the metal roof has been fading for the past several years. The fading started when the vehicle was about 1-2 years old, even when the vehicle was parked in a garage overnight. The vehicle was purchased in va and has been used in CA since 2006. We have about 110,000 miles on the vehicle. We have seen similar make/model Lexus Gx 470s that appear to have the same faded paint in the same ares on the vehicle as ours. In addition, the paint appears to be deteriorating and disappearing from the roof and on the edges of the doors. This could lead to rust problems. Our efforts to address this with the Lexus dealers have not met with success; the dealers more or less dismissed our complaint. Our body shop mechanic told us he believes the paint is defective.