I went this morning to the store looking for the tadpole gasket( they didn't have it in stock) and in the mean time I checked a Castile insert like mine and the gasket runs from top left to top right, no gasket on the top, mine it is the same. I have read in here that the gasket should be in both sides and at the top, so what is the right location since I'm going to install a new one? I'm confused. Thanks