After sleeping on it the only other things I could think of that will seep oil down the back of the engine would be the oil sending unit sensor, the cam cover gasket, and since yours is a 06 and has not been taken apart, it has the old style head gasket which might be seeping between the head and block in the back. Myself I am still betting on output drive bearings and seals. This could get pricey if your talking update kit because they have jumped to 1200 USD. If it were me I would take her apart and replace what is needed instead of the complete update kit. Not that the kit is not worth it.