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Assuming it's not an orginal, and I'm pretty sure this would work, you could spray it with a matte acrylic sealer. Not sure if cracking would occur, so I would test spray some material first, but I am pretty sure it wouldn't. I used acrylic matte sealer to stiffen hats and caps and no negative results so far. It should dull it down and would be waterproof. The fumes would require you doing this in a well ventilated area, of course. If original, or a Buzz, or RMNZ, etc., no way would I try this. Really, I like the shine. I think those really cheap Rothco MA-1s have a duller finish.