Re: C&C 30 mast step
The problem isn't the block of wood you see under the aluminum fitting, although that may need to be replaced also. The block of wood sits above the bilge on crosswise frames which are wood, and may be covered in glass. It's those frames which can rot out and need to be repaired. You need to remove the block of wood you can see in the photo to assess the integrity of the true mast step-- the frames in the bilge which hold all that stuff up.
1977 C&C 30 Mk 1 hailing from Port Clinton, Ohio