And rocker arms and balls? Stock rockers sometimes have horrible looking wear witness marks, especially with grooved balls.
For both new and good condition used stock rockers I lap the ball into it's socket with some diamond abrasive. Put a tapered spud into your drill press and spin it slowly. The ball will stick on the taper and you hold the rocker with your hands under it, working it around till it's smooth. Clean very well afterward to get rid of the diamond grit.
Necessary? I don't know but works for me. Try it sometime. Feel how rough the rocker ball is in it's socket on a brand new rocker. After a little lapping it's nice and smooth and has much greater contact area which should result in quieter operation and longer life. I believe the best outcome is when the ball naturally rotates while running, evenly distributing wear. Grooved balls and little contact area due manufacturing inaccuracy seems unlikely to encourage natural rotation.
