The 3.8 E's originally had a grease fitting on the side of the cast A-arm and had great lubrication - little a-arm wear. Then in '65 they put the grease fitting on the top cap with no pressure release hole next to it. Again, great lubrication. Then they used that top plate grease fitting with a pressure relief hole next to it (yours) and the ball doesn't get much lubrication. As soon as you put it in, it comes out the tiny hole. That's why series 2 upper A arms are all worn out. Whenever I get a plate like yours, I cut off the nail head end of an aluminum pop rivet and hammer it into the release hole. ( I have the plate out on an anvil, so the hole plug gets flat. )Now, when it gets greased, it goes all the way down to the ball.
Phil.