Your survey, with the sounding of the deck, and accompanied by the findings of the moisture meter will inform you. There is no way to diagnose this remotely.
Thing is, and it's not really brand-specific, a core repair on deck is not unusual on any boat after a decade or two.
IMHO, the EY factory did a way-above-average job of sealing every piece that they installed new (in 1988) on our deck.
The inside of the molded-in dorades on the the 38 and 35-3 were/are a moisture entry point until later repaired. A friend of mine had the interiors sealed on his '86 E-38, and there are narratives on this site. It was a rather Cleaver looking design idea, tho.
A mast base can eventually leak around the thru bolts, and under the deck layup in that area is plywood (I have observed this on ours). Normally, a repair involves installing a non-abxorbant coring like G10 or some form of thickened epoxy, from underneath. The original surface layup is strong, but needs coring for strength. There is a lot up up-force from the halyard turning blocks on the the collar, and that's why EY put a "tie rod" piece of short shroud wire on the inside to keep the deck at the mast base from moving. Our boat has this, with a turnbuckle on the inside.
Curiosity abounds -- is there a link for this boat (on Yachtworld, perhaps?