I removed the headlight, took it apart, and found the problem. Nothing broke and the second generation w126 adjusters don't use a ball and socket. The threads in the plastic adjuster knobs (see photo below) stripped out allowing the springs that hold the steel bucket in the plastic housing to pull the headlight's aim to the lowest and furthest right position.

The "T" shaped ends fit into slots on the steel headlight bucket and are held down when the lens unit is in place, then thread into the plastic adjustment knobs. Apparently what happens is that steel "bolts" corrode and in turning the adjusters in and out the threads get stripped. Fortunately I had another headlight. It was in bad shape and for the right side but the adjusters are the same. I took the other unit apart so I could remove the adjusters without unscrewing them then soaked them in penetrating oil overnight and the next day I was able to unscrew them without damaging the threads.

The other thing that can cause problems is that the steel bucket is resting on four protrusions in the back unit. They were originally lubed with white grease, but it was long ago dried up and the steel bucket was corroded. I cleaned the surfaces applied new white grease and now everything works very smoothly.

In case you're wondering, you turn the knobs to the right (clockwise) the raise the aim and to the left to lower it. It also helps to apply a little pressure to the top of the glass lens unit when you're turning the knob to ease the strain on the threads in the adjuster.

Adjusting laterally, turn the right side adjuster to the right (clockwise) the move the aim to the right, or to the left (counter clockwise) to move the aim to the left. On the left side turn to the right (clockwise) to move the aim to the left or right (counter clockwise) to move the aim to the right. When doing this adjustment applying a little pressure to the outside edge of the glass headlight unit helps ease the strain. There are springs holding the steel bucket into the plastic housing and they are pulling the aim down and toward the center of the car.

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2000 Mercedes S500
1990 Mercedes 560SEL
1970 Triumph Spitfire