Roof rails White misting

[Cooky]

Anyone else had this problem Only really noticeable on close inspection but a lot of the silver work I.e. roof rails and window surrounds have white misting on them MB claiming outside influence is the cause and not claim able under warranty. I only ever use auto glum products on my cars so unlikely to be that. Any retailers out there any idea how to remove. Been told it is plastic coated so polishing out not an option.