Thank you everyone. Now as I take a deep breath, it looks like I have 3 choices:

1. Sell the boat (any takers??? HI)
2. Open up the deck underneath the mast step and pour in filled epoxy and put mat on top and cover with mast step.
3. As above but fill the void using built up modern coring and filled epoxy.

The consensus seems to be that a solid area underneath the mast step is best. I am busy this weekend so by Monday, I think I will open up the deck in about a 5 in. circle. I will have to cut back my mast light and antenna lines as well. The open area will give me a good idea of what I am dealing with.

More to follow, I'm sure

What do I do to raise the ceiling in the cabin? Or should I just leave it as is ?