You are missing one of the guides that holds the window in place. It is a three piece part. There are two white nylon pieces about 2 inches long by about 3/8ths of an inch thick and both pieces are rectangular shaped. there is a small metal 1/8 th of an inch pin that is about 1/2 inch long that goes through the window and holds one of the white nylon pieces on each side of the glass where the hole is. There should also be a felt piece along the entire front of the window around the outside of the nylon assembly and sits inside the back of the vent window assembly. There are two of them nylon assemblies. One at the top where yours is not and another at the bottom.
Chas.
