The gasket in your Beckson opening port ensures that you have the proper seal against the elements. Keep your gasket surfaces clean using soapy water. Never use cleaning solutions on a Beckson port. Cleaning solutions will attack the product.
The installation instructions can be found here. Link
You sent me the wrong gasket is a common complaint. All Beckson opening port gaskets come rounded. This is an extruded material that has not taken the set of the window frame yet. All gaskets start out like this.