Brian, Can't speak for the mfg process of your version but on my 2004 you can clearly see from the pics above that the tank casting is glassed onto the hull. The pic of where the guy above has his left hand on the tank lid, is also detailed in the shot below it from my boat bilge and you can see that the lid is glassed down with heavy glass matt. I'd heard conversations about tanks being initially set in place with 5200 but it's hard to imagine that it'd be the final assembly connection for something so critical. If it failed you'd have to destroy the boat to get back at the joint. Properly glassed into place it'd stiffen the hull and act as another structural bulkhead(just a flooded bulkhead).
There are pockets and indentations up on the tank sides that could hold water until you rock the boat but that sounds like a lot of water. Look carefully at the tank pics to imagine how it aligns under the floor liner and then look for errant screws, moisture, cracks or damage. It's a pretty straight forward lid casting with only two upper penetrations, one at the compression post and another at the valve.
Most boats are built like a big Club sandwich. On ours the molded sections are layered together something like: Hull, tank lid, interior liner, tabbed cabinetry and then deck. The liner isnt really an integral part of the ballast in any way but it makes finding below deck leaks impossible.
The compression post has a SS fitting(also shown in the background of your CB pic behind the CB assy) that's glued/caulked to the tank riser where it sits on a matching riser in the hull where the CB bracket goes up into the hull. When you bolt the CB bracket in I believe it sandwiches the hull, SS compression post fitting and tank lid together. The interior floor liner is seperate and glued down to the tank/hull. I'd check the compression post base for leaks and caulk up both riser gaps between the floor liner and the risers to isolate any possibility of it's location.
I'm sure you'll find your leak and that it won't be a catastrophic issue. I just found my crazy rainy day leak(gal/hr) and it was a pin hole in the middle of the upper deck under a jib sheet where it dammed water, guiding it into the hole and couldn't be readily seen. For weeks I pulled out my hair and every deck fitting and all the windows were re-bedded before I spent 10seconds cramming a dot sized piece of butyl tape into the pinhole. Back to sanity.... at least my version
Good luck. Mike