I've had the cables from 3 sets of Sennheiser 212pros have one channel die within 3 weeks of each other. These had been working for 3-4 years (tested them all on my ipod, and swapped each channel where they plug into the cans to ensure it is indeed the cables).
Anyway I was thinking this is a very bizarre coincidence, so is there any possibility that it's what they're plugged into?
All it is is a DSE audio extension cable like http://www.noelleeming.co.nz/audio-.../prod66724.html (it too has been fine and used with these headphone cables for years); plain old 3.5mm, m end in the PC audio jack, f end with the headphone cable plugged in. It couldn't be...'overloading' cables plugged into it or something could it?
Otherwise this is a very weird coincidence.