New mikes that don't work? Are the folks fixing them aware of the workings of the mikes? There are a few things that can be got wrong.
Are the mikes genuine DC, or are they spurious parts from elsewhere?
It's worth finding out the spec of the "original" mike, and getting a replacement to the same spec if you want to do it "right".
If you're using it in a conventional aircraft, it doesn't even matter what headset the mike was designed for as long as it fits the headset you're using it with.