Seems to be standard practice to just silicone the tops of stuff on the sides. There should be a sealant like butyl tape between the window flange and the side.
When I have installed/replaced something on the exterior wall, I use butyl tape and finish with a bead of Lexel or Geocel all the way around. Sealed properly, there is no need to worry about moisture having a way out. There shouldn’t be any to begin with.
Sorry, donn0128, have to disagree. Maybe that’s the way it’s done in the great North-wet, but I’ve never heard of leaving the bottom of a window unsealed. Here, that would be like hanging out a welcome sign for all manner of bugs, especially ants and termites.
