For best results skim over both of the metal surfaces with a piece of emory cloth or fine wet and dry paper in order to clean up the surface and remove any high spots or traces of old cork / silicone gasket. Next apply an adequate layer of 'hylomar', or similar high temperature silicone sealant to both of the metallic surfaces. In this case, apply a bead to the the underside of the transfer box casing, then push your cork gasket onto that so that the silicone holds it in place. Next, apply a bead of silicone to the bottom plate, push it up against the cork gasket and bolt it on tight, ensuring that the cork gasket does not slip away from the outside edge of the two surfaces. Finally, apply gentle heat (with a hair drier) around the seal in order to help the silicone set. Leave it for at least 30 minutes before driving. That should do it!
-pos