Check out the photos courtesy of Dave M./gsxr:

http://www.meimann.com/images/mercedes/W123_suspension/

This is a W123 but the W126 is similar.

Replacing ball joints is not terribly difficult but it opens up a can of worms for related work.

I don't think you can get just the upper ball joint. You have to get the whole upper control arm which comes with a new ball joint and new bushings. You might as well replace the sway bar bushings while you have the upper control arm off.

The lower ball joint is pressed into the steering knuckle. You need a special tool to press the ball joint into the knuckle. You can rent the tool from ************************. A machine shop should be able to cobble up tool if they don't have one lying around. gsxr was able to press in the ball joint in with a generic tool by taking the ball joint dust cover off. I'm pretty sure you'll have to take the brake rotor and shield off for tool clearance so think about new rotors.

If the ball joints are worn, there will be some improvement when you replace them. However, worn ball joints usually mean worn lower control arm bushings and control arm bushings as well. Think about how much work you want to do now vs how many times you want to take the suspension apart.

The spring only has to be compressed to replace the lower control arm bushings.

Sixto
91 300SE
87 300SDL
83 300SD