Jim:
Thanks for your response.
I looked at my loader, there is an o-ring on the left cylinder. It's out at the end of the ram. The one I found on the ground must have come off the right side. Once I knew it came off the loader, I checked the manual. On page 50-3, under assembly instructions, there is a picture of them. The caption says "Cut paint mask rings off all cylinders". Mystery solved.