Just as a follow up I had my RH rudder lower bearing replaced recently.
Upon
removal, which was rather difficult it appears that the
aluminum outer bearing has corroded and seized the inner
race in it.
The shaft has then turned on the inner
race and worn to a large degree.
I think it would be a long while before it failed but the clunking
noise is rather annoying when you are try to sleep at night.
I also noticed that there is some crevice
corrosion starting on the shaft which I think will lead to shaft failure so I'm going to invest in some earthing leads.
This design is flawed and I will be looking at making up something like cat man do suggested as a permanent fix.