I did this same thing to mine, but the center pin also came out.
I twisted the antenna off the part below the blue line in that picture using two pairs of pliers (and some electrical tape around the parts to mitigate damage from the pliers).
Then I dug out as much of the Loctite as I could. Mine had a little ball of it touching the pin inside the connector, which I assume is why the pin came out too.
I ended up pulling the pin all the way out of the connector so I could clean it, so when I re-inserted it I didn't go all the way in coz I wanted to make sure it made connection to the circuit board when I put it back in the radio hole. Then I screwed it down as best as I could using a dime (I don't even know what the proper tool for these rings is, and my needlenose pliers are too fat for the grooves). Eventually the pin came up and hit the dime so I had to improvise from that point on with a small screwdriver. But at least I know it's touching the circuit board where it should.
Then the brass ring had to go on, and it has a rubber ring underneath it to seal the whole thing up and make it submersible. Again, I had to improvise with a small screwdriver but I got it as tight as I could.
The radio works like it should. And I can change antennas now. I'm just not sure it's submersible anymore since I wasn't able to tighten everything as tight as I would like to. And I don't know if maybe I should have put something on the center pin to seal that part up as well. But the actual radio works just as well as it did when I got it.