I just started digging into this. It looks like the ferro fluid was mostly non existent. Im really having issues getting the voicecoil gap to be even around the magnet assembly. It seems to have shifted and boy is it tough getting it lined up again. Seems to want to snap back to an uncentered position.
Reassembled with new ferro and the original diaphragm. Hoping to give a test run tomorrow.
If the pole piece and or the top plate has shifted that is whole other level of repair, if repairable. With the gap visibility uneven
that driver is not going to sound like it should, if the pole piece slips anymore with the diaphragm installed it could ruin the good diaphragm.
Sounds like that driver took a good bump, losing some of it's magnetic strength or both.
If the pole piece is not longer fixed in the center of the magnet that driver trash. There are places that will demagnetize, recenter and reglue old unobtanium drivers like JBL 2440s but the cost is more than a replacement for most modern drivers. Buy a new one.