Most of the problems found with leather Pickelhauben come from drying out and shrinking. Dry conditions or hot situations cause the leather to dry out, lose natural oils, stiffen and shrink. In OR’s helmets, extreme dryness causes “red rot” where the liner basically dissolves into red dust.
Shrinkage causes broken visor trim, bent spines, broken solder pins, missing shellac and sunken shell tops. In addition, shrinkage breaks the stitches holding the visors on to the shell. The shell itself shrinks inward until it looks like a deflated football. An excessively hot environment will melt the shellac finish on the outside of the helmet and cause it to run. Cloth uberzugs in these hot conditions, will absorb the melted shellac and stick to the helmet. These are my observations after 4 decades of collecting and restoring these helmets.