So, it appears that I was able to repair my Pro1-X's radios.
Previously, telephony and mobile data wouldn't work for me, as documented earlier in this thread. WiFi, Bluetooth and GPS had always worked perfectly.
It turned out that my Pro1X was missing most of its "antenna" connector springs. My main antenna (aka. USB) board was missing two of its three connectors, and the last one broke off while I was diagnosing the problem. See picture attached.
It appears these things are really fragile. Also my "diversity" antenna board was missing one connector, which I found rattling in a