I completely agree with the OP. My 7506s were unbelievable when they were new. But they have been left in a drawer for 3 or 4 years because I have only been using loudspeakers lately.
Last week I had to do some accurate vinyl ripping so I pulled them out and... surprise!!!! Not only the earpads were crumbling (literally), but the sound had changed in a way I couldn't explain: bass and midbass completely gone, treble harsh and overwhelming as if I were listening to loudspeakers with foam suspension damaged.
Luckily enough in the same drawer I had my old AKG 240 monitor, that I had abandoned for the Sony: less punchy and tight than the Japanese wreck, but still reliable after more than 15 years.
