I just saw a episode of This Old House where they installed a replacement vinyl window. It was a casement window. The flashing was part of the window and was an extension of the vinyl. The old sill pan had been renmoved because they said it was not needed. The window is installed by shimming to the correct height and level. Then the flashing was nailed to the rough opening to attach the window. Next they went around the window with roofing felt. I believe this was caulked first. Next, a special window flashing fabric (looked like shiney plastic) was applied. I think it was self adhesive. Finally, the trim and sill were snapped into place (also part of the window made by the manufacturer) and the edges were caulked. A third grader could have done it.
If it were me, I would want something better than butyl caulk.
Is this better than the old way?