... The broker didn’t seem too worried about...
Why should he be worried?
Go to a good shipyard ask them how much they will charge for a complete repair and deduce it from the price of the boat.
High humidity content leads to delamination over the years, no matter how it looks on the outside, especially if it is a cored deck as most are. If the water is there for a long time (more than 6 years) the problem is much worse than if it was a recent event.