I have an M50 with aluminum thermostat housing. The back is routed out for the funky orange rubber gasket which I have. The side that interfaces with the t-stat doesn't have any routing out and looks like it uses the o-ring from the t-stat to seal or something. I also bought a gasket that fully covers the entire thermostat housing, its green - i forget if I use the big full cover gasket with the plastic housing or what. Basically, I have all the thermostat housing gaskets which do I use with the aluminum housing?