The point of failure on the older models is pretty uniform: The ear cups are held to the headband by eyeglass screws threaded into a plastic retainer, eventually the plastic thread gives way and the ear cup comes off. Here's what mine looked like, and another redditor's, and a third for good measure.

I'm not trying to belabor the point, it's just that the HE-4XX is my favorite headphone so far and I wish I'd put zip ties on them, so I'm trying to show you very specifically where the problem is, I guess. Sorry, I'll go.