I found the advertisement on Ebay of the helmet originally posted in this thread and I have to admit that it looks really good. It would be very difficult to argue authenticity with this piece.
Here is another example that is different than any of those above:
https://www.ebay.com/itm/Rare-Antique-Bavarian-Officers-Mohawk-Plume-not-spike-Helmet/292893851692?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649
Note how the front and rear visor are attached under a leather bead unlike the one in the original post or the one in James' collection.
I wish that I still had the photos of the fake that I once purchased. It was made from one of these:
https://www.ebay.com/itm/Antique-Imperial-German-Firemans-Firefighters-Leather-Helmet/223121095350?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649
I bought it off of Ebay and didn't question any of the photos; it looked good. When it arrived I found that the Raupe was made of fake fur (nylon I believe) and that the cockade was actually plastic. The outline of the comb used on the fireman's helmet was still visible on the inside of the helmet (couldn't be seen in the ad photos because of the silk liner and it was covered on the outside by the Raupe). It was beautiful --- just not real. It also became the absolute worst nightmare that I have ever had trying to return something on Ebay. The owner guaranteed originality (which wasn't true) and I had to prove otherwise. The seller simply stated that he didn't know. To make a long story short, I was able to return it and I got my full purchase price. Since it came from Germany I was out around $100.00 for postage. A lesson well learned.
Again, now that I have seen photos of the inside and all angles of the helmet in question, I would say it does look original!
James --- I have got to buy that book!
John