Next Up: Wiper Linkage Bushings!

The collar you can see from outside isn't really a seal. Its just a filler for the void. This way they didn't have to exactly align the various body parts. Any water that gets past this collar goes into the cowl only. The seal that stops water from coming into the cab is sandwiched underneath, where the pivot mounts. All that will be a lot clearer after you remove the pivot assemblies.
One tip... Mark the bottom of the pivots with a sharpie before you remove them. Install the grease fittings opposite side from the mark, then install them rotated 180 degrees from where they were. This puts a worn spot on the shaft against a unworn part of the bronze bushing inside. Unless the inside is just totally shot ( more common with left side pivots ), this will eliminate more than half the looseness, thus smoother, quieter operation.
You would have to take a pivot assembly apart to see/understand where and how they wear inside, what this tip is all about.