Thank you Peter.
My issue is with Galvanic corrosion between the carbon and the alloy rudder stock casting. I have read the link, this indicates that the issue was sorted 6 months after production started, my boat is 4 years old, which is well away from the first production boats. So using GRP and paste clearly does not solve the problem.
Initially I did speak to RS and emailed them a picture. They still said I would have to buy a new assembly. Not very good when this is a design problem, not a usage or care issue