It is counterintuitive they would machine a groove and then not use that groove for an O-ring.
The drawing previously posted in this thread clearly shows a seal placed in each of the two grooves
that same drawing does not identify any component as being a bushing
that drawing is for a Ford pick up of similar vintage to our Pantera‘s. Is it possible there were different versions of this shuttle valve?
photographs can be deceptive. Are the O-rings the same size or is one larger than the other? If they are the same size then they are both designed to go in a groove. If one is larger than the other than it would seem to follow that it does not go in a groove but remains on the piston
I will say this again as it is the reason we are having this …..looooong ….discussion
take photographs whenever you take something apart.
Larry