I haven't done this, so advice is based on what I've read! Adjust confidence accordingly.....
It may be the nearby stanchion, or some other fitting or crack, that's letting the water in. Regardless, you need to do two things - dry out the deck and stop water from getting in.
You can use a small mallet or the butt of a screwdriver to sound the area, and see how much water intrusion you have (by the change in sound when you tap on the deck). If it's a tiny amount and there doesn't seem to be any deck delamination, you may be able to drill some holes and flood the area with acetone to dry it out.
If it's been happening for a long time, and the deck is delaminated and/or the core rotting, you'll know because the deck will be spongy when you tread on it, and it will have a distinct dull thump when you tap on it. If that's the case, you'll need to do a much more extensive repair by carefully cutting off the top skin, peeling it away, scooping out the rotten core, drying it out, and installing new core. There are a few excellent books on doing this; I suggest Don Casey's "This Old Boat," or his "Hull and Deck Repairs."
You'll also need to properly reattach the deck fittings in the area, which means you need to
- remove the fittings
- redrill the holes using an over-sized bit
- route out the core material around the holes
- tape the bottom hole closed and fill with epoxy
- redrill the fitting holes
- reinstall the fitting, bedded with a sealant
Again, Casey's book, or other maintenance books, go into great depth on how to do this.
BTW, I'll be repairing a large soft spot in my deck at the fall haul-out. I'll take lots of pictures and post them.