Putting the car back together after a clutch job and had to replace a failed slave cylinder. When I got to the car today I found that someone had removed the old one and had the line capped. No one has any idea of o-rings coming out with it, and there was nothing stuck in the old one, so I picked up the grommet kit that comes with two o-rings and two cup washers...

The question is this... Am I only using the cup washer in the slave cylinder or do I need an o-ring and the cup washer? The exploded view doesn't show anything and since I didn't pull it out I'm at a loss.