Is there house wrap over the sheathing now?

I would use butyl flashing because the Andersen DH windows have a nailing fin that is not sealed to the frame and there are usealed openings at the upper corners where the nailing fins are cut at the overlap of the fins. Andersen says these joints must be sealed by the installer but no one seems to do it. The easiest way to seal these joints is to allow perimeter self-adhering flashing to roll up onto the frame enough to seal the nail fin joints. This exposes the flashing edge to the sealant between the window trim and the frame. Asphalt-based flashings can be dissolved by the plasticizers in some sealants (like Ceocel 2300) causing an unsightly mess. WR Grace and DuPont make butyl-based flashings (Grace Ultra and StraightFlash respectively).

If you mean a "drip cap", it should be placed over the top of the window trim and the air/weather barrier should overlap it.