I tried various monitor/mixing phones over the years, and I found I kept coming back to my AKG 240s. I'm still using a pair that I bought over 20 years ago, and I didn't notice any deterioration of the drivers. I had the wiring come loose on one of them, which fortunately I was able to repair, but they've been remarkably robust. I note that these are the K240M version with 600 ohm impedance - it takes a headphone amp to make them sound full, but perhaps this makes them more robust. I also own newer K240S (lower impedence, louder and more transparent with low-output headphone jacks) and K271s (sealed backs which I only use when recording with mics that would pick up leakage from the semi-open 240s). The thing about the AKGs isn't just the absolute sound quality, which is very good but not the best I've ever heard. It's about the combination of excellent sound with light weight and comfort. I can use them for hours and hours, which I haven't found to be as true of other brands/models I've tried. This is the first I've heard of loss of sound quality over time, though of course depending on use/storage conditions, any headphones will wear out, eventually.