[pestes]

So just to close this out - thanks to everyone for their help and ideas.

It seems that my decision to not assign immediate importance to the roof vent cover was not to blame.

And once again, Richard was correct. I found at least 2 places around the window frame that were leaking, both leading to the front lower corner of the frame before coming out both on and behind the wall paper.

One place was literally right next to the point of ingress and you can visibly see a gap in the butyl rubber behind the outside of the frame. The other was less obvious - right near the top center of the window frame, along a seam in the aluminum bus shell. The shell was slightly pushed in at this spot, enough for water to get behind the frame.

After putting a bead of sealant all the way around, I sprayed it for quite a while yesterday with no new ingress. As soon as I can get it in to someone who can do the work, I plan to have the window frame pulled out and reseated with a new seal so that the thin bead is not the only thing between us and the rain.