Being on a tiny island, somewhat nestled in the last century, things like silicone sealer are not available, but being an island, with lots of boats, marine epoxy is.
So i spent some time draining the tank, and jamming epoxy where the panel appeared to be separated, inside and out.

also took the opportunity, with the water level down, to catch the tetras with parasitic Lernaea, and pull the copepods off. One was so embeded, the upper half of the caudal fin came off with it.

There are some close up shots of the parasite in the disease section.
Whether or not the seal holds, only time will tell.