G'day mate,
common problem from poor preparation during fitment of parts.
To prevent problem re-occuring you need to clean all components down and insulate the disimilar metals.
On my 2004 Seajay i removed all the fittings and applied Tefgel which is a teflon/silicon insulator to the threads and mating surfaces.
This product is one of many available to do this job and it is well worth the few time taken.