I owned an 82 Maramu (Hull 102) for 16 years before switching to a
SuperMaramu in 2001 and had a similar leak. The water pipes for the forward head run
through a PVC pipe that goes through the bilge compartments just to the port side
of the keel, While in Japan I had a fresh water leak similar to what you
describe. After isolating various pipes and checking the cycle time of the
freshwater pump, I traced the leak to the copper coldwater pipe to the foward head.
Since the pipe was in the PVC pipe I could not access or replace it, so I
decided to bypass it using a flexible hose. When I cut into the PVC pipe I was very
lucky to discover a very small crack in the coppper pipe, almost certainly
caused by freezing. So, instead of bypassing the entire pipe I just replaced a
small section. Problem solved.
Hope this helps.
S/V MALAIKA II