If I remember correctly, that pad is just a wedge of plywood. A replacement wouldn't need to be any fancier than that.

The sides of the pad are tabbed to the cabin ceiling. That fiberglass tabbing can crack or seperate from the pad. If that's all you're seeing, don't worry about it, its not important.

I would pull some loose tabbing away and see if the pad is rotten. Maybe its actually a deck core problem.

Got any pics? Is the mast off?