I saw the helmet photos a week ago. Sadly, the leather helmet body is in very, very poor condition, basically "relic" condition. I didn't jump on it because for me there are too many issues with it.
The helmet could be one of only 2-different things: It could be an early 1st Guard Regiment of the Foot helmet since it has a fluted spike. Or, it could have been a Prussian General a la suite helmet.
For me personally, the helmet is only worth the sum of the salvageable metal parts on it. The leather body has literally been almost destroyed, and it is probably hard as a rock from the couple photos I've seen of it.
The eagle is missing the crown from it's head, which kills the value of the eagle front plate. However, the guard star looks to be in good shape, and would be salvageable.
The leather on the back side of the chinscales looks to be in very rough condition.
Leather helmet body has a large hole in top center of the helmet. The front visor, and a large portion of the forehead area of the leather helmet body are missing. I believe the section of leather on each side where the chinscales would attach to the helmet are also missing or split out and away from the helmet body, both things that are not good.
Brian Loree who owns this website forum can do miracles with helmets. But this one would be a real challenge and also expensive to try to bring back to any presentable shape, in my humble opinion.
Hope this helps. It's sad to see a helmet like this that was entirely neglected and abused over the years. It probably had a lot of kids that played with it and broke it up over the decades.
Best Regards,
Alan