I had the same thing on my hunter 23', 1987. I removed the nut and washer one at a time. cleaned up the area and bolt, dried it off and put a bead of 3m 5200 marine caulling. you can get this at home depot for 1/2 the cost of west marine. i use the fast drying version. this fixed my problem and the boat is dry as a bone.
You may want to take a swim under your boat and check the area where teh keel meets the hull. I just scraped my keel and botton 2 weeks ago and was expecting to find bad things, but it was in very good shape. boat still needs a bottom job though.
dave