From my email archives:
The part # CR 19778 is for an oil seal (CR is for Chicago Rawhide - the manufacturer). The seal has a spring around the inside of the rubber lip. That spring is a perfect replacement for the starter sprag spring in the starter sprag assembly. Throw the seal away and keep the spring... that's all you need.
Here is the detail from Chicago Rawhide:
http://tinyurl.com/bfu9l
This seal is for a 2" (50MM) shaft so the spring that is inside the seal is what you need for the starter sprag. I have yet to make this repair myself. Just going by the research that I have done in "preparation" for this one day.