The oil comes up through the cylinder head and reaches the hydraulic unit through a small hole in the threads where they screw in. Over time they seem lose their internal seal. Then when they sit w/o pressure, they "leak down" and clatter until they fill with oil again. Sometimes the seal is not achieved and they clatter when warm. The clatter happens because the element cannot hold the rocker tight enough against the cam.

If you have this problem with new elements, you can try a thicker "hockey puck" to increase the pressure against the cam. Sometimes rocker or cam wear can cause noise as well.

__________________
Chuck Taylor
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