I think you need to try the other checks you already mentioned before it is possible to know if the problem is in the headset itself or the radio. Particularly using the suspect headset in the P2 side, and the P2 headset in the P1 side, and the other radio. Since you state that comm between P1-P2 is OK, that steers me to think it is not the headset, but the other tests will prove that.
- GY