re-seal keel bolt on I28

[skkeith]

I just exposed one of the keel bolts on my 1975 Islander 28. It was covered with what I assume was epoxy, more like rust oil residue. Flaking that off the bolt and nut are show here. Some of the thread distortion is camera angle, it was a hard shot, but there is erosion of the bolt to some degree giving it a slightly concave shape, while still having intact threads more or less.

Is this something to worry about? I just had a diver look at the keel and there is no visible 'simile'.

What should I use to re-seal this and is there any particular technique? Any advice, I have never done this before. Thanks in advance!