Neicy, there is no purpose to placing barrier coat on a lead keel. Barrier coat is normally placed on the fiberglass of the hull to prevent water entry into the material. So, you have some confused information. Not knowing what previous owners may have done toyour boat, it might be worth having a surveyor or other trusted party take a look when you haul, and noting things down in writing.
Usually the keel-hull joint is bare and exposed, and on many boats there is some slight crack there after a number of years, and sometimes weepage through it. That would be a classic "leaking keel" joint, made worse if the keel had impacted something in a collision or in a lightly built racing boat where simple inertia had loosened it up over the years, as it tacked back and forth thousands of times.
Sealing over the top of the keel bolts inside the boat is a mixed blessing. A great idea for keeping bilge water off the bolts--but a terrible idea since any water that gets to them, is equally well trapped on them. And damp stainless steel is subject to rather horrid failures, the term is generally "crevice failure" or "anoxic corrosion". In the absence of oxygen, and the presence of stagnant water, stainless can crack and fail quite suddenly.
Personally? I'd get that fiberglass cover off them and examine them, and if you are at all unsure of their condition, get them surveyed professionally. Many builders use plain carbon steel washers or carbon steel nuts on the keel bolts--and if those rust, they are easily replaced. When you are done, you may want to protect the bolts again. Tar, beeswax, paint
, all can be used. Themore durable they are, the harder they are to remove for reinspection. Beeswax has the advantage of being cheap, easy to clean, easy to apply or remove.