Island Packet 27 sole damage. Why?

[CrazyRu]

I hope anyone familiar with the model can chime in.
I’m searching for IP27 for friends who are out of states.
Apparently the model has peculiar damage seen across all boats I have checked so far.
There is water damage/rot going all the way around head compartment on outer walls. At cabin sole and vertical walls joint. There is no obvious points of entry for the water. I’m pretty sure that in the last boat I checked nobody used shower for 20 years. I have heard the explanation that old water and holding tanks could leak. However last boat I checked has updated tanks. More over. I checked the boat first time about month ago and the area was dry. It is wet now, after a few days of storms. So it must be a leak. But where?
Does anyone have an answer?