I am having trouble with the center support. With the thinnest selectable washer it will not seat all the way. The center support goes in all the way if I leave out the washer between it and the direct drum. With the washer in it stops in the middle of the snap ring groove in the case. I have double checked the assembly of the rear section. I am thinking maybe I have an oversized washer? How thick is the center supposrt to direct drum washer supposed to be?