Many thanks for that. This sounds ‘near identical’ to my current 1979 Mk 11 problem. This certainly does help me !! I will refer to your experience closely when I further dig into the affected area to find the root cause.
Its a pretty nasty problem and looks a bit costly too. However I am over whelmed by the helpful and generous feedback I am getting from the association. As a result I no longer feel so worried about tackling it.
Poole Yacht Club