Yes I would like to add an o-ring to flange. Currently I'm having the prototype flanges (7 different versions) water jetted from my CAD files. I can't add a groove unless I have the flanges machined, which currently I have found to be more expensive working against the desired price point. Everything is a give and take I guess. As Matt posted below the current Nissan gasket has a sort of "O-Ring" on it. Have you had trouble with these as well? In my experience a little bit of Grey RTV Silicone on both sides of the gasket help make the seal as well.
