i purchased the o ring and back up washer for the lift pump piston along with a lift plate repair kit. i dint know that a o ring and back up washer came in the repair kit but the back up washer is leather in that one. what would the preferred back up washer be leather or rubber? if the leather one is used, would the finished side face the o ring or face away from the o ring. and what is the trick to getting them on there? coat them in oil and soak the leather in water?