It is making a noise because the ball stud - aka hydraulic lash compensator - is not holding the rocker against the cam. The ball studs are pre-loaded and there are a shims that come in various thicknesses that control the pre-load. The thicker the shim, the greater the pre-load. You can have good ball studs that need thicker shims, or you can have worn out ball studs that need to be replaced. Either condition can cause valve noise.
MB makes a special tool to adjust the pre-load.
My point about the rockers was that unless the cam lobe was worn, I did not find them to be worn as I worked my way through valve problems on the Wayward Woman (380SL).
If you want too much information on this, try a search on "hockey puck" or "ball stud."
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe