I have a 98' 258 Vista. Water marks have been present on the ceiling of the liner, the false wall between the anchor locker and the cabin, and occasionally when it really rains it rolls down on the sides. I had just about exhaused all areas I thought water was coming from. Then this past weekend I removed the entire hatch and found that the brown water stains were caused by the rotting wood core.

The water must have been running between the inner and outer fiberglass skin. It found a way out through some type of penetration in the inner skin between the hatch and the bow. Which then allowed it to leave nice water stains.
Should I remove the wood that is damaged?
What do I put back in its place?
Can I do this without removing the liner and the inner fiberglass skin?
Thanks for the advice.
Ben