Re: Help pinpointing a leak
C & C's do not have wood in the sump. Keel stub is solid fiberglass laminate. Use of additional washers was not uncommon if stud thread did not extend down far enough.
The laminated in place frames/stringers were layed up over foam forms, the same stuff florists use to stick stems in floral arrangements. For form only, not structural. After years of water & bilge debris penetrating it will deteriorate, but the laminated structure remains intact.
Owner should be evaluating cause of keel being loose (not just that it is loose) - severe previous impact (look for fairing repair at bottom leading edge of keel, upper aft edge, laminated frame/stringer repairs in sump) or keel bolt deterioration. Any experienced yard familiar with this type of construction will look at these as first & second obvious causes. The smile is enhanced in your case due to loose keel spliting the fairing material on the joint.
Keel bolts don't undo themselves. There is an underlying cause. Aside from any undetermined structural repairs it is a nuts & bolts installation with an sealing/bonding material between. Finished off with refairing, barrier coat & antifouling.
Talk implying how easy it is to do aside - it is labor intensive, requires the right equipment, and often includes grinding to bare glass to create clean bonding surface. IMHO don't discount this as an unskilled labor project. Experienced yard skills are needed.