What a life this helmet must have lived. I believe it is an Austrian m1917 helmet, but I am not very familiar with WWI helmets so I an not completely confident its Austrian. It was refurbished and issued to the Reichswehr with apple green paints and double decals. It was later refurbished in the standard 1940 pattern with textured paint and a single decal. You can still make out the apple green paint and the tricolor decal under the top layer of paint. At some point the vent lugs were broken off; this seems to have been done quite a long time ago. It looks almost like one of the dents might have been from a hammer or something when the person was trying to remove the lugs and missed. The helmet has a few small dents and is generally well worn. There is not much of either decal left to speak of. You can barely make out the wing tips of the eagle. The only markings are a crudely stamped 66.
The liner is basically complete but there is a hole in the leather at the back and it is pulling away from the band a bit at the front. I would not put weight on the liner. There is no drawstring.
Considering the obviously rough life this helmet has had, it is in pretty good condition. It was issued on at least 3 separate occasions before coming home with some GI.