Just to close out the loop, we figured out what the problem is.
For the F4001s, you could tighten down the screws finger tight and the earpiece would work fine.
However, for the other radios, you had to use a screwdriver to tighten them completely down. Finger tight would keep the transmit from working. After tightening them completely down, the TX worked fine.
Weird, but at least i've got a solution!