I have had to caulk windows every year on my 4 year old house. The window are Vinyl Milgards and the trim is wood like composite. The first year I used a Dow elastomeric 50 year caulk, then the polyurethane but it was not a good brand. Then I used Sidewinder.
Maybe it is my technique or maybe I should call my painter buddy who just gor devorced................. Anyone want to comment? What about the paintable exterior silicon? Oh the gaps are opening up on the window edge not the trim.