Panzer IV Question

You are referring to the muffler. The muffler was made of thin sheet metal and was exposed to drastic temperature changes. I assume these factors made it corrode rather fast. The same thing seems to happen to a lot of car mufflers; actually this happens to any muffler that I can think of.

Heat tends to oxidize ferrous metals faster than anything else. Can't go wrong with a rusty muffler unless it's brand new.