In the spring of 2020 I made a repair top the deck core around the partners on my 10M. The partners is the hole in the deck that the mast fits through. The core around this hole was cored with plywood. In low sunlight you can see the outline of the plywood core on the deck. The edge of this hole gets worked a lot by the mast flexing against it's wedges. Several years ago I had sealed the edge of this hole with epoxy but the constant working was too much for that seal and it failed allowing water to get in and rot the plywood. In retrospect I should have routed out maybe 3/4" of the plywood and filled with solid fiberglass. Now the rot was reaching back a couple inches. I dug out all the rot using a cordless drill with an end mill in the chuck. This did a very good job and I kept at it until I was getting dry chips. Then I measured the extent of what I had removed and cut some blocks of solid 3/4" thick fiberglass to fit. I glued that in place in a mash of thickened epoxy.