My 1979 boat, early on used to weep from hairline cracks (4 or so inches from the hull) where the hull molding stops and the keel is bolted on.. What I did was ground down the glass that covers the hull/keel joint and ground our the gap. Inspected for potential problems with the bolts and then epoxied the joint back together and faired it. This was part of an overall keel fairing to the minimums allowed using class templates.
We did ours back in the early 80's and we were getting rust stains then, so I don't think I'd panic just yet.
You might contact randy Borges at Waterline Systems too and pick his brain. There is also a lot of information on prepping old boats at the J24 Class Association website and there is a forum there too. Lot's of knowledge.
http://waterlinesystems.com/boats/j24/
http://www.j24usa.com/
And, we did pull the vermiculite out of tha cabin sole. There is a kit to redo the base and cabin sole.
Great Boat! I raced mine for 30 years before selling it and buying the Beneteau.
Enjoy.
JRacer
OutraJe - USA 1427