Any question answered...

I'd bear John Lewis in mind. Pair of my Sennheiser's stopped playing out of one channel, took them back, they had a listen and gave me a straight swap there and then. Didn't even ask about me mistreating them, which I hadn't anyway. Can't quibble with that.

Also +100 on the Sennheisers. And it can be worth paying a little extra to get after sales service. Or, at the other extreme, one could try to source them direct and unbranded through eBay from the factory that makes them, à la carbon frames and wheels....

My HD414s are 2.5 decades (approx) old and still sound as good as new, only replaced the foams about every decade.