The 6.4 powerstroke rocker arms have had some trouble. The rocker arms are prone to breaking or having the tips wear out. This happens because of the way that the rockers lack oil lubrication. The designs is the same as the 6.0 powerstroke but the 6.0 power stroke does not have this issues. I have actually had the valve cover off and watched to see if they were lubricating and the river of oil that is supposed to lubricate just is not sufficient. This repair is not to bad as long as it does not damage any valves.