Hello, I have a pair of very old Sennheiser HD 520. The sound is still quite good although they could use a 50000 miles service... (they need new pads mostly.)
On the cup, there is a tiny plastic piece which goes into the headband. On one cup it was broken into two pieces, one still in the headband. The other cup, the headband, and the cables are all intact.
I fixed it last weekend. Superglue (loctite superglue precision), and I was happy... for two days.
The surface between the two parts is small. I don't give up easily... so now "ROUND TWO".
I glued it together again, then added drops of the glue on top of the fix, and let it dry, and then new drops, dry, new drops, dry. My idea was to form thicker "plastic" around the weak part, hopefully increasing the strength of the fix.
Not sure if my idea makes sense, but I suspect superglue isn't optimal for that idea: The adhesive action took seconds, but the open drops took an hour each to dry.
I just now realized that it looks possible to separate the cup from the headband first, for easier handling. Doh.
As I am pretty sure I need to do it again soon... any hints how to it like a pro?