I will NEVER buy a boat with ANY end grain balsa in it ANYWHERE. Been there never, never again.
sounds like the voice of experience. Some details might help others understand the issue.
Look at end grain balsa mats at the fiberglass store. Then imagine what happens if you have water intrusion. If it is a vertical surface the water will drain to the low spot and rot there. If it is a horozonal surface, like a deck on a boat the water will run to the low spot stay there until the trim changes. The gaps between the balsa gives the water canals and "freedom to move around the country" setting up rot everywhere.
While EGB is light, stiff and properly applied and maintained it is excellent but one non thinking, ignorant or don't give a damn individual works on the surface then failure is eminent. Case in point, the Mainship 34 MKI, II, III. 78 to 85. Boats were shipped to dealers, bridge furniture, ladders, deck rails, bridge shield and other attachments were slapped on. No hole saw and filling beforehand where drilling was to take place, just 'git er done. That is the beginning, and I bet you know the rest of the story.
I took 5 or more Home Depot buckets of saturated mush out before recoring the bridge, similar on the cockpit and various soft spots on other decks. Every one of the Boats in that 7+ year production run I have encountered had exactly the same issues. Never, never again.