I have a pair of Sony MDR-7506 headphones which are at least 17 years old. (Somehow they ended up in my possession after an acrimonious breakup with a girlfriend. It's possible she was the original purchaser, but it could also have been that she inherited them from an earlier boyfriend. Oh to be young again.)

After many years of use the outer lining on the ear pads disintegrated, so I bought replacement pads from Rubber Monkey. Unfortunately these replacement pads had a much shorter lifespan and the lining began disintegrating very quickly. 

Does anyone have any ideas where I can find replacement ear pads which aren't going to begin dissolving themselves after a couple of months? I don't use these heavily or regularly, so I'm unsure why the replacements degraded so fast.