SJC.Welcome to irv2
Where you see the black wood is the wood wet or falling apart, is the wall paper falling off panelling, an is there any seal left around outside lite fixture? You need to fine where the leak is first.
You could remove the whole wall panel if you think your fiber glass or bead board is all wet. Where your panels butt you may have a trim strip that if removed will reveal the staples holding on the panel to wood stud, just pry off panel carefully to elimiate damage to panel.
Some times if you push on panel you will see heads of staples that can be removed. If you have any papers on construction of your Lance it may help to give you an idea what your up against. Even a call to Lance they could give some advice. If your lucky an the panel and inside is not wet now you may just have to fix the leak.