Thanks for the responses. I'll try and get some pictures posted so you can see it. This may take a while as I need to work out how so please be patient - I'll be back!
Thoughts on Dave's comments:
The joint does take quite a bit of stress, mainly latitudinally ie: at right angles to the shaft.
Regarding the type of glue - sorry I don't know. It looked like some thermosetting compound to me. Something the guy who fixed it generally uses when fixing beams in houses. I fancy the salt water played a part in corroding this but I may be wrong. There was no "finish" to protect it and his compound may not usually be exposed to salt water.
In hindsight the guy that fixed it did a bit of a bodge and made up for lack of accuracy in the fit of the carbon rod in the drilled hole by using the glue as padding if this makes sense. After weeks of searching for help I was very grateful to find him so don't want to knock him. His trade is beam repairs in houses rather than close joinery.
Thoughts on Rob's comments:
Please excuse my ignorance - I can't follow the description due to my lack of knowledge of your craft. It sounds a sophisticated repair the likes of which I was hoping I might find first time around. Might it still be possible over the broken first attempt? It also sounds the sort of thing that's way beyond my skillset - Wish I'd found someone like you when I was searching for local help. You're not exactly local to me! How much work is involved in your suggestion? (Time). Would it need specific timber type or would any old (reasonable grade) wood do? If I try and find someone local to do this what type of craftsman am I best looking for: Joiner, Carpenter, Woodworker, something else??
Look forward to hearing more and will research how to get the pics posted.