[pestes]

So, the leak we encountered in the bedroom is definitely due to sealing around the window frame. I found 2 specific spots where I could cause water ingress with a hose. For the moment I've applied sealant externally but ultimately plan to remove the window frame and reinstall with a new round of butyl tape.

However the question now stands as to the existing damage. Here's a picture of where the water ingress point was under the corner of the window frame and where it ran down the wall. There is a bit of mold here obviously after pulling the wall paper off.

Any opinions on whether this can be treated or if we need to replace this section of plywood in the outer wall?

If replacement is necessary - how difficult a job is that? Will the foam layer in the wall get damaged by removing the plywood? I also worry that this particular sheet disappears behind the left bedroom wall. The stain stops before the wall but I worry replacement would require replacing the entire sheet, including what is behind the laminate wall.