When I removed the cams and rockers and stuff from my donor engine, I had to remove some retaining spring clips from the rocker that attached to the ball stud. (See below photos)
Item number 3 in the first image is the spring location, and the second image shows the variance between engine types.
I took photos of my camshafts when I was diagnosing a noise, and at the time wasn't aware of the springs, then later I was looking at the images again and noticed the absence of the springs.

Attached Thumbnails

   

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RIP: 80 300SD
RIP: 79 450SEL
2002 E430 4matic (212,000km)
2002 ML500 'sport'

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