It now appears that it's cheaper to throw away busted noise reduction headsets than to repair them.  Check out the recent article from Onboard Updates:

Effective immediately, please discard any malfunctioning noise reduction headset, including those currently provisioned in United First and United Business cabins on three-class B747, B767MZ, and B777 airplanes.

While these headsets remain a high value item, repair costs have escalated beyond the cost of replacement. Please continue to handle noise reduction headsets with care by using provisioned tote bags.

The January 2004 Flight Attendant Operations Manual revision will reflect this change.

I wonder what lucky landfill gets those!