The adaptors I linked to will plug into the existing socket on the Metrix and provide a BNC or F type without altering the unit.
The center contact of the Metrix probably just needs a clean and maybe a gentle squeeze together of the split.
Thanks for actually be willing to help, rather than judge, that's refreshing. If only they could all be like you, how friendly and productive TEA would be, not to mention the SNR would skyrocket.
I grabbed my LED torch light and threw some serious Lumens into that socket, I noticed that the two halves of the split inner core were actually joining at their very bottom, it's in fact one single piece of metal. Therefore it did not make sense that one half was giving me a signal and not the other. Had to be bad connection. And when I saw the staggering amount of crust covering 100% of all surfaces in that socket, all black in there, thick layer.... it further reinforced the hypothesis. So I did what I could to clean it. Attacked it first with a tiny flat screw driver to break up most of the black crust, blew some human air in there to force the debris out. Then flooded the socket with contact cleaner / Deoxit, agitated it with the stiff hair of a nylon brush. That loosened the remaining crap. Then using the screw driver again, I managed to shove a kitchen paper towel deep into the socket to dry it and take all the debris out.
Now looks soooooooooo much better ! Shiny and clean, almost like new. What I thought was "patina" from a distance, was in fact just crust and nothing else.
Fired up the scope and generator, now works much better.....
Will order a BNC adapter and see how it goes, but should do it I think...