That's fair, I suppose.

Me, I only ever tried one pair of Sennheiser headphones, HD660S. And I disliked them. The sound was good, but everything else wasn't. Very cheap feeling plastic, it squeaked annoyingly every time I moved my jaw, or even head in general. Since they were open, I heard that squeaking all the time & it drove me mad. Heck, even my old ATH-M50 headphones (original ones, not even an X version) felt a lot more premium with their build quality and materials. HD660S felt like a good, $300 sound within a horrid, $10 housing. Suffice to say I never bought Sennheiser again.

I wouldn't even bother fixing it, honestly speaking. I'd just return them & get another pair, from another brand. If a company allows this, has poor QC and this shit happens fairly common, they don't deserve your money. Just my opinion on the matter. :)

By getting a new pair of headphones. :)