Secondary diaphragm housing gasket

I am changing my secondary spring to a lighter one to as you know to open them up a bit faster a tuning thing.There are 3 pics one with a gasket that does not cover very much on the housing to seal,or I can use a rubber o ring that sits in the housing and is above the top enough to seal.When I pulled the housing off lost the gasket,so not sure witch way to go.In my old instructions #105 says gasket, does it sit flat on the housing or in the reset of the housing.