It is kind of ironic, but I have found that a thick layer of bar oil/chips/sludge covering an old magnesium saw seem to offer a better degree of protection from the elements as compared to a clean-as-a-whistle saw that has been sitting for years. It is like cosmoline for metal. One of the worst things to do to a magnesium saw is to leave it sitting directly on top of concrete, especially if there is any moisture present. The underside will corrode away like crazy once the paint has been scratched or worn away. Noticed on the pic of the 250 that the rubber spark plug cover is missing. That is required so as to keep the air flow from the flywheel blowing across the cylinder head so as not to overheat the saw. Otherwise, a good deal of the cooling air just blows out of that opening. The covers were used on a wide variety of Mac saws & kart motors. They had been in such demand that they have been brought back as an aftermarket replacement item.