The Spec TOB comes with an o-ring. It's not supposed to be installed with it. Do not know why it comes with it. You also need to use anaerobic gasket maker. NOT RTV.

http://www.shop.com/op/aprod-p23915377-k24-g4-~anaerobic+gasket+maker-nover?sourceid=13

-'96 SE MTX 3L -'98 SVT 1,173 of 6,535 -'05 Mazda 6s, loaded, g/f's ride -Need a 96-00 manual on CD? PM or email me