We had a Historic FF2000 press day at Brands in December a couple of years ago and the salted track surface certainly played havoc with magnesium Hewland gearbox casings. I have seen the same thing with a car that's been towed on an open trailer on a salted motorway. A very thorough wash down, a lot of compressed air to blow away the water afterwards, followed by repeated daily applications of WD40 over the next week or two minimises the damage but won't necessarily restore the appearance.
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