Professional advice was taken before starting and during the job and you should do the same.
A weep from the aft keelbolt.
The weep meant a breach in the hull to keel join but this was easy to find as the place was marked by a small patch of rust and cracking in the antifouling at the after end of the keel on the starboard side. The gap was revealed with a scraper.
The rest of the join was good and there was no other cracking, not even on the port side aft. The offending gap was cleaned and left to dry out. Zethar had been epoxied in 1986 and a skin of epoxy covered the hull to keel join,