For me I found that it was the little metal piece between the main glass that rolls up and down and the triangle glass on the door. I took a piece of wood that I put in the window frame and gently bumped it up to space out the top of the metal a bit and the window moved a bit better. Ultimately I ended up unscrewing it at the top after you remove the rubber gasket and bumping it over significantly. I then slotted the screw hole and screwed it in place with the wood holding the aluminum in place.
My window works great now!