Just to resurrect this issue, and make it known that AKGs response to this matter is completely unsatisfactory.
I had them replace the original set of phones that were broken, but actually had to give them back to the person who gave them to me since I had no receipt. They were really insistent on this point.
The second set of phones broke again, after very occasional use, and they just collected dust. I really missed having a quality set of headphones around, and decided to take action. But while Googling for AKGs site, you can see the internet is absolutely LITTERED with the complaint about this weak point that holds the headband to the swivel mount that attaches to the phone.
After half a dozen e-mails fencing with them for a return, Harman basically told me to sod off. This, after a cat and mouse game trying to find the serial number. (It's under one of the ear pads)
I was really pissed. But wait, there's more!
Not only is the 490NC flawed this way, and the company had to KNOW since they got a flood of returns and complaints, they simply duplicated the design on the successor model, the N60 NC. This complaint for that model appears right on AKG's website:
"$250, that is what I spent. What I got was structural design that is beneath what should be excellence from Germanic/Austrian engineering. Firstly everything is great about this headset, and I don't want to take away anything from the fine engineers that did the good stuff. However, it means nothing when there is a bad apple in the mix the renders the entire headset garbage. The problem: the only thing connecting the earpiece to the headband is a very weak piece of plastic. From what I can see, it is also not fixable. So, my perfectly working N60's, made garbage by a piece of plastic. Engineering fail with the cost put on the consumer."
The guy happens to be right. The phones have a great sound signature, but they can't even stand up to light use, i.e., I never even traveled with them and used them exclusively at home. In the meantime, you can imagine how gingerly I handled the replacement set, and they still broke. So not only was AKG aware that the 490 was flawed, they kept right on producing them with the flawed design and carried it through to their next model.
The N60 is still being sold on their site.
AKG has a good rep in the field. But I think I'll avoid the brand from here on in.