Here is the Herr Fuchs finger test:
Helps to have a remote switch for the starter.
For each cylinder, place the cam lobe pointing up. Slide your index finger between the bottom of the rocker and the ridge of the ball stud. Mentally note the gap - like 4 mm. Now rotate the cam lobe down. Feel the gap. If it changed more than "a little bit," the HLC is weak.
After you have done a few, you get a better feeling for what the gap should be.
Note that if the rocker is down - like only a 1 mm gap - with the cam tip up, it is collapsed.
You need a 24 mm (I think - check this first) deep-well socket to remove the ball studs.
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