A power sliding back window assembly for a motor vehicle is provided. The assembly can include a window casing with a first window pane and a second window pane fixedly attached thereto. Also included can be a generally U-shaped guide rail that has a first end and an oppositely disposed second end. A third window pane having a portion or edge fixedly attached to a glass carrier can also be included. A first cap can be attached to and located at least partially within the first end of the generally U-shaped guide rail and a second cap can be attached to and located at least partially within the second end of the generally U-shaped guide rail.