I replaced the pads on my AKG Q701 headphones today for the 4th time. It made me realize that I’ve used these headphones for at least 40 hours a week for 14 years straight. I’ve had to repair the left side speaker solder joint a few times, but they’re designed to be easily torn down and repaired. Truly BIFL headphones.
I’ve heard that the newer AKG K702 headphones are identical but I can’t vouch for that. They go for around $250.
With use and age membranes change and the sound changes with it. Unfortunately you’d still need to change the driver / membrane combo on a regular basis if you want to keep the sound quality of these cans.
This is true for any cans, and AKG are on the long-life side of headphones.