Yes, as Steve says.....NO SUN !! Being black in colour, these things heat up very quickly and this heat further dries up the natural oils in the leather and melts the shellac coating on the exterior surfaces. Period photos show that all of these helmets had a shiny patent leather finish on them when new. However, with 100+ years of shrinking/drying out during the winter and then expanding with a humid summer this natural finish cracks, sometimes pops off or if you are lucky, just goes "dull".
The shell contracts in on itself, as in this case...then the front visor trim can split and break. Another typical result is that the rear spine is flattened where it goes over the shell and the soldered split brad holding it on pops off. The leather and it's shellac finish are totally "organic" and natural and react to climate conditions. The metal is not, all it can do is split, or break. The stitching thread is 100% cotton, so it rots or also breaks with the expansion/contraction of the leather. These are the common problems and the reasons for them. How to "hydrate" your helmet is described in the restoration section. If you have further questions, please ask. You have a nice M95 helmet marked to the 12th Infantry Regiment, any other markings?