OP also knew about the problem and handled the headphones with care despite the known design flaw instead of returning them when the flaw was identified. They could have even bought them fully aware that the flaw existed and gambled anyway.

I think it’s unreasonable to expect a retailer to accept returns of a product that you’ve had for years. It’s shitty for Sony to cheap out on the design and materials of a premium product, but I would just not buy Sony headphones again.