Z400 question

[RIDE-RED 250r]

I have an '03 Z400. Was changing the oil and filter today and unlike other Suzukis I own, there seems to be no O-ring that goes on the oil filter mount inside. My old 230's have a small O-ring there but there was not one on this 400. My question is, is there supposed to be one there? I have looked at parts schematics on Bike Bandit, and it doesnt show one. It only shows the large o-ring on the oil filter housing cover, no small one inside where the oil filter fits over that post. It looks to me like there isnt supposed to be one, but if anyone could confirm that for me I would appreciate it.
Thanks