I’m just replacing the original group head gasket after a year of ownership just as a preventive maintenance.

The original is flat on both faces, the Cafelat blue replacement is flat on one face but the other has slight chamfered edges. Any advice which side should be the one that contacts the portafilter?

Slight chamfer on inner edge of seal goes to the top. FYI on other machines with basket type screen the chamfer accommodates the slight flange on the screen.

    Thanks, makes sense now why there is the chamfer