dull mottled exterior trim in E55

I have a 2001 E55. The exterior trim pieces around the door windows and front and rear windshields are discolored and mottled. The dealer replaced all the trim at his cost but the same thing has happened again. The Benz representative is going to look at it in 2-3 weeks. Has anyone reported this problem? Have you any idea of what could be the cause? I can't think of any unususal environmental factors except that I have run my car through a spray automatic car wash on a few occasions. I have a Harley, Cadillac and Honda Accord in the garage and the E55 is the only problem so I doubt the cause is with my garage.