Funny you should ask, I spent Sunday pulling out the window on the street side of our Trillium
because I had investigated every thing else first. When looking from outside, the left side of the window frame (towards the front of the trailer) and the bottom left part of the frame was wet. The water was running between the wood frame and the fiberglass, then running down between the ensolite and fiberglass, sometimes ending up on the bench, but most often running all the way down into the storage area underneath. I have included pictures that show where the water was running.
The other spot I had very bad leaking, a prior owner had replace the electric cable entry cover poorly, and water was streaming in there, and when there was enough water, it would travel under the fridge
into the area under the front bench. I forgot to take pictures of that.
As for the black strip, sorry I don't know, but would replace a few of mine if I could find it.