I purchased from steambright a pumptech 500psi regulator repair kit for one of my portablesM500, it came with a piston black rubber that goes on the piston and another metal ring with a rubber in the middle. I am trying to figure out does the round ring with rubber go in first and than piston? I am not sure! Or just piston? Not sure if this peace is something extra they send for other similar machines. Can you help?