Tom Perera, the owner of the Enigma Museum — a company devoted to locating, restoring,
preserving, and trading German Enigma machines as well as antique
cipher, telegraph, scientific, and communications devices — has just issued an urgent warning about a serious case of corrosion in some Enigma machine. The source of the corrosion seems to be coming from one type of the plastic light filter that these particular machines are fitted with. The light filter is usually fitted in the lid of the machines and it is strongly suspected that these filters are generating Acetic acid vapours that will build up within the case when the lid is closed and then attack all close by nickel and copper parts.
I hope this photo will convince you of the seriousness of this corrosion problem and that it will make you visit Tom Perera's Enigma Corrosion Web page for more detailed information and how you can prevent this happening to your own Enigma machine(s).