Ah, moisture meters....
Reading a moisture meter is sort of an art, not a science. Unless you have lots of experience using a reliable and calibrated moisture meter, I would be very careful about taking any action other than getting an expert with a calibrated meter to give you a second opinion. If you both agree that you have a wet deck or core, you might want to try the West System for repair before doing anything as radical as cutting out a piece of deck and replacing the core. I've had good luck on a previous boat by merely marking off the area where I thought the core was compromised, and then drilling a pattern of holes all over that area. You need to make a jig for the drill so you only drill into the core, not all the way through. Dry out each hole with acetone. Then fill each hole with epoxy from a syringe. Finally, dab some gel coat on the tops of the holes. This can work if the area is not too big or the core extremely wet. It is worth trying before anything radical like cutting the deck out is attempted.