I was replacing foam door gasket with taller one, when I noticed it. The doors are all FG bay floors plastic sheeting so now other issues. Luckily no issue plywood was skin above the rot was probably just poor sealing not much paint on end grain. Looks like they used 5/8" ish x 3" plywood filler strip at fiberglass upper seal bezel and maybe sealed with resin and painted.
I would have to split replacement pine/treated wood or pvc exterior trim in half or possibly use two layers thinner delrin or other man made material. Thoughts are just insta-foam it, dress the outer area and use polyurethane sealer. Foam the backside use smaller filler piece and then sealer. The rest look good maybe one next to it has been filled with a lot of sealer at some point. That one is piano hinge at top, not pano door. Piano hinge door doesn't need any relief for outer lip of fiberglass pano door.
Pics ...Bad one..and about how the rest look,green paint is not needed others are/were satin black various amount of green overspray. I might be slipping a nice heavy coat of paint on the rest to make sure they stay sealed.
Other ideas I have thought of.