Greig I did what your doing one at a time as well, but I got mine done before it got wet. It is something that had to be done as we are keeping the boat for a long time. I guess it was a way of cutting cost at the time Catalina was making our year of boats.
Randy

Later On Catalina figured that out and I think they put epoxy on all the exposed core where things go through the deck. Not sure about my chainplate deck holes but I do know Catalina epoxied the exposed core on the areas where my opening ports were. I happen to have a 1999 C36. Not sure when they started doing it.

Definitely not done on the 95's, though at some point in time a PO had wisely ground the core out at the chainplates and filled with epoxy. I had to redo a couple of them because they didn't go deep enough. I am now doing the same thing to the stanchion bases, did the front 4 over the winter and will do the remainder next winter.

Even with the core filled you're still not home free with water ingress, even though our deck tested OK around the chainplates I found the bulkhead on the starboard side was rotten at the bottom from water running down the back of the big SS chainplate. Any leaking in a cored deck is a serious issue as far as I'm concerned.