May I suggest that you show those pictures to:
http://www.rotdoctor.com/ ?
They are used to dealing with wood rot and mold, as their specialty is repairing wood damage on boats.
They will undoubtedly suggest CPES (Clear Penetrating Epoxy Sealer) as a part of how to treat your damage. It will cost a bit; but, will probably be worth it. CPES was originally made to combat rot and mold problems; and then, they found out how good it is and started using it all over. It's very easy to use.
It looks to me like the plywood was not sealed properly in the first place nor was the trim properly sealed. So, you will want to take all the trim off and deal with the damage and prevent future damage now. Otherwise, it may simply continue to get worse. ...My 2 cents.
PS. The Rot Doc is used to dealing with teardrops, too.