My keel repair work looks remarkably similar to Conundrum. Fixing the junction at the tail of the sump to hull connection because of a grounding. I've ground mine down quite a bit more though. I'm recoring around the keel and planning a full fairing job.

There is a 1/8 to 3/16 inch of material between the bottom of the stump and the top of the lead. The filling in the sandwich. A few voids and some areas of separation between the "filling and the bread." I'm sure this could let quite a bit seep into the sump if the "band-aid" around the sump to lead joint has loosened and produced "keel-smile."

I really don't see a reason to drop and rebed the keel. The sump and bolts are very strong for the size and weight of the keel. Overbuilt like many other parts of the boat. I'd strip the joint down to the molded sump and lead and do a G-Flex keel-smile repair. retork the bolts to spec when that done. That's what I'm doing anyway.

The sump was molded into the hull in the original layup. It is in two parts just like the hull. the outer "skin of the sump is nothing more than mat and two layers of woven roving. This is laid over the inside of hull laminate skin on both sides with hull core on top of it. Most of the sump thickness comes from when they tabbed the sump in over the inner skin when the hull halves were put together. The sump is 7/8th thick on the sides and 1.25" thick on the bottom. Half that is probably more than enough (my opinion but I am not a marine architect). There are plenty of boats floating with much less sump thickness and more lead.

Anyway, the crack you're seeing is from the joint at the outer skin of the sump where the two halves come together. There can be voids at the joint. It's not structural if that's all it is. When I stripped the gelcoat of my bottom I found a void at the center line hull joint running all the way from the front of the sump to the bow. Void as in air.