Are you SURE it's actually rust? Electric sabre masks are supposed to use stainless-steel, and that is VERY difficult to corrode...
Try scrubbing the spots with a toothbrush. If that doesn't work you may have to get a wire brush; sabre masks are just bare metal so don't worry about taking off any insulation as with a foil mask. Be sure to have the areas punch-tested afterward.
Has it been around any reddish clothing? Sweatshirts/pants? Towels?
I had a big patch on my mask once that LOOKED like corrosion, but on really close examination turned out to have been very fine and caked-on lint. It seemed to have gotten oily somehow and congealed into the mesh.
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