Check out
www.rotdoctor.com By the looks of it a ton can be accomplished using that stuff. I have played with it a bunch and went so far as to drill holes in my transom dry it out and saturate the ply then fill the holes in. Cool stuff works well as far as I can tell. It pushes the water out and makes it so the wood there will never rot. Look back through the questions asked on their web site and ask the doctor your self they are great about getting back to you. Early in the season like this I'd hate to delve into a big project. If you do replace it I would treat the new wood with CPES before putting it in the boat.
Good luck!