As you can see, the flux ring is no longer vibrating.
VERY very very carefully remove the cone and spider with a small flathead screwdriver without damaging them; this takes about 2-3 hours... takes patience borderlining on insanity, no less.
Then use the wood handle of a painters fan brush (any non-magnetic substance really) to confirm the loosest side of the ring.
Grab your superglue and a toothpick.
Insert the toothpick into the top of the ring on an angle and drop drips of superglue into the crevasse via the toothpick.
Be VERY very very careful not to get any excess glue on the gap walls, you only have 0.25mm or so of motor clearance. (Or the toothpick stuck)
Reattach cone and spider with more glue, make sure it is centered to the n-th degree +-0.5mm
These things are far too good at generating infrasound to just throw them away; not only that, but they are almost at expensive as LMS-18's!!!
Without the repair they make nasty super-annoying metallic noise, similar to that of bottoming or rub; but it's niether, it's actually Lenz's Law of EMF backforce vibrating the loose ring around, made worse by coil heat, over time.
I'm just happy with the thought of getting all 17 of my subwoofers back up and running again... this is gonna take years,
Right now I'm only running 5 subwoofers, by summer I should have 9 going (maybe); I've changed my mind on box designs, multiple singular sealed scattered throughout the room is the way to go.