The Sony MDR-XB950BT Headphones are really nice and comfy but they appear to somewhat frail.
I purchased 2 and both broke in the exact same way.
The swivels that hold the earpieces in place at both ends of the headband are prone to break and it is very difficult to fix "elegantly".
To use this replacement you have to cut and sand the broken swivel off the black plastic piece (be careful not to damage the wire)
Then you superglue these 2 prints to the end of that piece making sure the wire goes through the hole the middle (be careful not to glue the wire to the printed parts).
Let the glue dry well and then re-attach the earpiece bracket to the swivel using as it was supposed to.
I have only just fixed mine, and it looks well. not sure how permanent this solution is, but at the very least you don't have to run to buy a replacement.
Black is possible
Printed this with a 0.6 nozzle but you can go lower if you want