When I installed mine I assembled the both pieces via the connector clip. You could see the connector clip position from all years of those pieces being together. I lined those up, used 3m black butyl tape, rolled between palms to about 1/4 bead, then placed that in the center of the trim right where the screws go, going the full length from one end to the other, over lapping where they meet. Start in the corner, using a awl to find the screw holes. Get the corner in place first, that corners not moving, not adjustable. (well maybe big hammer) There should be clear indentations in the channel where the screws bent the WSC when tightened down originally. Get all the screw in and snug up evenly. If you use to much butyl tape it'll ooze out and is mess to remove. I used white pipe dope tape, about 1/8" thick 3/4" wide on my first attempt. That's how I know about the 1/4 bead. I had that white crap everywhere and the white stuck out like waving a flag. Hope this helped didn't confuse your more.