The legs on the screen fit into the groove in the port frame. The gasket should be placed with the seam at the top of the window. Push the leg of the gasket into the groove at the two corners of one end and then slightly stretching it, do the two corners on the other end. Then press in the rest and you are finished. Make sure the gasket is in correctly.
All manufacturers use an extruded gasket which is bonded in a loop.
Since the bond point could interfere with the seal, we place this at the top of the window. A person removing and re-installing the gasket may not have noticed this. Resist the urge to share it with your ports. If you find yourself using an aerosol can of CRC or WD-40 or other lubricant, don't spray the hinges. If you are cleaning the galley with a spray cleaner, don't clean the lens.