These are in such a position that removal is not possible without removing the u-joint. They are up against the hub of the half shaft..... No means to get in there....it was a battle with just a skinny screwdriver trying to get the excess grease out!
I can only surmise that with problems related to "over greasing" and the mess in the engine compartment, that this was some sort of device to let a user know that the u-joint was potentially full...... again, perhaps from a vendor that was trying to provide a "fix"......
Steve