Hi WD, same thing here, "modern" helmets are often junk after 4, 5 years max,
while "vintage" helmets may suffer wear and tear from use, but are structurally much hardier.
Unfortunately, vintage helmets will not pass the stringent survival tests and will shatter your skull...
Still... I wish I had never thrown my 1984 Nava racing helmet, the velvety liner was trash, but the shell was fiberglass and the padding fitted me like a glove.
You could
sleep with it on, it was that comfortable !