So as many others over the years, the headband on my Audiotechnia ATH-M50's started to crack and flake off..
I had previously modified these to be removable cable (using 3.5mm jack) and as such sending them to AT for repair wasn't an option I contacted Audiotechnia and purchased the headband assembly (part 381303270 $23.65 + $13.01 shipping).
The new assembly arrived today installing it isn't too hard you must remove 4x screws by hing / arms on ear cups then de-solder 2x wires (positive top right / ground bottom right) and 1x additional screw holding earcup to old headband.
Once earcups removed then reverse the process screwing new headband on and soldering wires of new headband on.
Here is a video overview of the process.. good way to restore your old m50's and of course keep stuff out of the e-waste.
and a photo of the M50's back in action: