This is the larger of the two capitol D food grade hollow silicone gaskets. It sits on the lower flat part of the interlocking lip.
We have them custom extruded out of a special high-tech, high-temp resistant food grade silicone.
Use black Permatex Auto silicone gasket maker to attach, installation instructions in the private KK forum owner's maintenance area.
Amazon: Permatex 81158 Black Silicone Adhesive Sealant,