I don't believe that one way sprag bearing is worn as bad as you may think. Those rollers are likely shaped the way they are on pourpose and act on a cam-lock principle. If you take a look at the "rollers", they appear to be pinned and pivot from the center (note the gap on each side of the center of the roller). The outsides have to flats, with one side being longer than the other. The shorter side is further away from the pivot point, however, so when the gear turns in the direction of the shorter - longer - flat side, it slips. When it rotates the other way it cams over to the smaller - taller - flat side and causes it to grab, and since the rollers are oblong shaped, it applies force to both sides and locks it all up.
That's my guess on it's operation at least.
If the shoulder and higher/shorter side is worn enough, or if the inside of the gear is worn enough, it would prevent sufficient or consistent lockup and cause it to slip, and it wouldn't take much wear to cause it.