Why didn't you buy a gaming chair just for info.
Apparently the older austrian made ones are better. Issues started appearing when production moved to china. It doesn't effect the sound at all. Just build quality and cheaper materials in the plastic causing friction and squeaking. If the choice is between a mediocre overpriced headset vs the best headphones that money can buy for cheap that requires a little modding then I can live with that.
I have toyed with the idea of putting glue into the crack but that is permanent and would restrict movement / comfort. It's not proper cardboard either it was a card much like a business card cut thinly to size and then jammed into the crevice. You can't even tell it's there now.
You can get a knitted cover off aliexpress for like £1.50 shipped. The same covers on ebay are 10 times that. I went for an all black one with buttons. It's went from being death bumps to only sore if you wear for an all nighter. I need to get some cotton wool or foam and then glue it or position well then put the knitted cover over it. The knitted covers are very neat looking and protect the headband.
Plus my lime Q701's always get compliments but I know some people won't like an luminous green headphone.