You DO need a special tool for removing the rocker arm to replace the lifter, (hydraulic compensator). How did you inspect the rocker arms without removing them? The wear takes place under the cam lobe, where it interacts with the rocker arm. The oiling problem you just solved may have left you with worn rocker arms. You may wish to invest in this tool, and remove the rocker arms where they are tapping. Look for a wear pattern on the arm, matching the cam lobe. Replacing the rocker arms eliminated the tapping on my 560SEL, without replacing the cam, (risking pulled head bolt threads). Of course, Mercedes says to replace the cam with the rocker arms. Good luck!