I use a product called QuickSteel. It starts as a putty, you knead it and it becomes moldable. Mold it around the swivel part (however your headphones will no longer swivel but that is the price we pay for being Sony MDR-XB950 owners, they are easily broken.) [br]
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I permanently fixed mine to a permanent position. It kinda sucks but it works. I painted the dried QuickSteel with black paint and it matches the rest of the headphones however it’s not the most prettiest option.