Wise move. The stub joint should not appear to be compromised, which is what the photo shows. Many years ago ours looked like yours. I had the yard lift the boat off of the keel, clean the joint surfaces and re-bed with 3M-5200. That was in 2004. The stub joint remains solid and sealed to this day after cruising many thousands of miles.
What caused it to look like that is hard to say, but considering the way Hunter builds their boats I would suspect the keel hit something with enough force to open the stub joint seal.
Trying to seal it from the outside without dropping the keel and re-bedding is only a temporary fix. It appears from the photo there is water inside the joint cavity. Also, make sure that the yard inspects the keel bolts for stretch that might have resulted from a hit force. If so, the yard can add a thick shim washer to the keel bolts so that the bolt nut is raised into fresh threads.