It's a nice M1915 shell but not worth $1675.
The problems that I see are:
1) No liner.
2) The wappen is conviniently missing the loop that would show it doesn't fit the helmet correctly.
3) Some one was working very hard and very poorly to get the original wappen mounting nuts off. Notice the bulge in the middle of the right wappen postern hole, formed bythe thread of wappen mount as it was forced into the helmet.
4) The wappen isn't looking too good.
John