Hank,
You might try drying the flooring out. You would be surprised at how long  
marine grade ply wood can withstand water. Once dry, it may retain much of it's  
original strength.
If you do have to replace it, the only wood to use is marine grade plywood,  
3/4 inch if memory serves me. You might have to special order it from Lowe's 
or  Home Depot as I doubt that they stock any.
My bet is that the seals around the front opening ports are sealing. From  
there it's a crap shoot.
 
Rummy