I also have some Pro4aa bought new a few years ago (I unzip the box). Headphones had been in the store for about a thousand years. 😁
Despite being new, the inside of the pads had "volatilized" and one of the drivers was not hearing well due to dust on the pad. I was able to send them to the Peninsula (continental Spain) and with the Koss guarantee I replaced the driver that did not work.
being honest ... they sound horrible and are quite uncomfortable, the plastic coating of the earpads is hard and sticks with sweat, but they are indestructible