I've got a vintage pair of Sennheiser HD-520s, MkI version, bought back in 1985/6 (struggling to remember which it was...)
I've already replaced the pads/foam covers once and now they need replacing again - looked at them closely while replying about another posters worn out HD-470s covers.
The question is, should I replace them or replace/upgrade them to something newer. I do like the full-ear covering, opened-backed Senns, they're very comfortable to wear and I only use them at home, so appearance is not important, nor noise leakage. It's been so long since I looked at headphones, I have no idea what cost to get equivalents would be and whether, in today's terms, the HD-520s are any good. Just for completeness, the cans have had fairly light usage over the past 25 years, only really being brought out for late night listening when it would have upset the neighbours.