E30-1 Mast Step

I acquired my E30-1 (#123, 1969), last spring at a storage auction with the mast stepped. I replaced the lowers last summer and am planning to address a problem at the mast step while I install a base plate for turning blocks.

The mast step has sunk into the cabin top approximately 1/4". The area around the step is solid, and several small test holes were dry. It appears that there is a layer of core (plywood or similar) on top of the mast support beam that has crushed over time. If anyone has had this area open I would appreciate knowing what lies beneath. Is it plywood? The top layer of the mast support beam? I would take some pictures but it is too d*** cold and icy.

Thanks in advance
Richard Friend

Do a search on this, as there are excellent posts including pictures from other owners who have replaced/reinforced this area, and did a great job at it.
Good luck!
Frank