I don't know if it matters or not but
I would guess that the side with the groove would be on top so the most surface contact would be on the bottom when the shaft is at rest and no force is applied I.E. normal driving with the hubs unlocked. Reason being that if the shaft can rattle from bumps and vibration it won't damage the bushing with more contact to the shaft. This principle is used with heavy duty truck spring bushings since they don't use rubber bushings and they go for lots-o-miles.
This is just a guess but a logical one...I think.
what'd you think?
