I have (2) D12e, one works perfect, the other one does not, makes no pops when it plugged up, also by touching any of the wires inside makes no buzz or hum, simply dead, even though the capsule may be dead or not, could it have another issue by no buzz, ground hum etc ?
Best person to work on that mic would be Richard Land of Land Audio Services in Hendersonville TN. He has a web site AKG Mic Repair. His phone is 615-338-4443. If he can get the parts, he can fix it. He has a long history with AKG and has access to more spare parts than anyone else I know of.
Richard is your best bet in the states, but AKG have exhausted their stock of parts for the D12E so it might be difficult to fix. I'd imagine any tech would be able to test the microphone and tell you if the capsule has failed.