Just to be clear, is this the traditional metal plug or a Gortex plug?

Yes you could repair it with some thickened epoxy. You probably need to remove the whole thing to get the epoxy all the way around.

If the plug wobbles after you tighten it, you might have damaged the plastic threads in the board. Like others have said, the vent has a plastic/rubber seal. That seal presses against the board to prevent water ingress:




That gap between the board and the circumference of the plug is normal. When you sail, a tiny bit of water pools there because the sealing happens a little bit below the surface of the board.
check the seal (o-ring) and check the plastic threads and report back.

^^^ this

but it needs to be a good temperature increase to be sure

speaking of sure - how certain are u that the insert itself is moving in the board, not just the screw is wobbly in the insert? If the insert is loose it's going to need to come out in its entirety and be replaced. Just gluing around the top will seal it up maybe, but it won't be properly bonded to the board and will fail again. It's not a hard DIY with a holesaw and new chinook insert

I wouldn't even wait 15 mins to heat up. I would put soapy water immediately after putting the board under the sun.

^^^^ that's a great way of learning about it and figuring out how it works and what it should (or shouldn't) look like.

Btw, you can use the same method if you have a ding in your board and want to know if your board takes on water or if it's just superficial. Just make sure your vent plug is closed in this case. If you have a Goretex vent plug (the plastic ones that work automatically) put some blue tack around it to seal it up when you're testing for other leaks.