If this isn't caused by Newday777's observation:
Parts 22, 11 and 4 in the diagram are parts for the spring pack that lightly seats all the plates to prevent them from sticking or 'chattering' when the oil is cold, too thin, or very old (as in, parked too long, so plates stuck together). They are part of the overall height of the clutch pack. If they are missing, they are hard to come by: you might then consider installing and extra steel plate in their place (or maybe 2 of them) or else an extra fiber plate and steel plate, to take up the space. Otherwise the clutch springs will not have enough force to close the clutch pack when the lever is released, and it will slip.