"Fungi" which receives pressure passes from the membrane into the gas node. Top nut presses the sleeve to the axis of "fungus". It simply unscrews.
The membrane is intact. Probably just soured "fungus" and was in no hurry to return to his seat, when you turn off the water. Since Kit was purchased in its entirety, and change the membrane and other small Circuits. Change the "fungus" not see any sense, because the plastic will not rot and rust like metal, which is in the Repair Kit.
The plastic sleeve from the top also replace. Smazhem new grease from the inside, where the axis is moving. Tightening the nut with a new hub does not drag, see that the axis can move with little resistance. Is not very small and the water can flow at this location.