One way to check the Lower Ball Joint is to support the Lower Control Arm on a Jack Stand high enought to lift the Wheel off of the Ground with enough room for a "Bottle" Hydraulic jack to go under the bottom of the Steering Knuckle (Tire needs to be removed to do this I think).

If the Joint is good as you pump the Hydraulic Jack you should see no upward movement of the Steering Knuckle.
the same might be done with a Pry Bar but if you are by yourself it is harder to observe. A Book I have shows using a Pry Bar under the Tire to pry it upwards but you cannot do that and look at the Joint.

The same Book shows the type of Ball Joint and Spring setup the Mercedes has tells you to move the tire up and down to find the Ball Joint Play not rocking the Tire in and out.

Not sure how to check the Upper Ball Joint. Depending on how the Car is jacked up the Sway/Torsion Bar is going to put pressure on the Arm.

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84 300D, 82 Volvo 244Gl Diesel