[rohrmann]

What you are seeing is the squeezed out butyl caulk tape drying out. Over time, I developed leaks on three of our windows, not from the cracking where it squeezed out and dried, but where the butyl caulking had shrunk, leaving a microscopic separation between the window frame and the wall of the trailer or slide wall. What I did was, using a plastic putty knife, removed all the dried caulking from around the window frames and used black silicone caulk to run a bead all the way around all the windows. Haven't had a leak since. I figured, yes, maybe the proper way would be to remove the windows and install new butyl caulk tape and re-install the windows, but eventually the new tape would do the same thing as the old tape and I would be dealing with leaks again in the future.