I've seen a dismantled MZ-5n and it is totally plastic.
Mine must be the rare one with metal inside then, I also have an even rarer MZ-3 with metal inside 8)
According to Richard Hunecke's books about the MZ-5/3/5n (sorry if I have mispelled his name, I have one of my cats on my lap and cannot go to check it) the internal chassis of those cameras is made of metal (light alloy diecast).
Carlos
