Clean the steering box well then watch carefully for the source of the leak. Pay particular attention to the hose connections into the box, the adjustment screw atop the box and the input shaft from the steering column. There's also the plug for the steering lock at the bottom of the box. I thought mine was leaking from the pitman arm shaft seal, and very likely it was, but it was also leaking from the lower pitman arm shaft lower bearing carrier.

http://www.peachparts.com/shopforum/showthread.php?t=239322

Since that fix, my steering box is leaking from the steering box adjustment screw. I guess the seal didn't like supporting the full weight of the pitman arm shaft. I hope I can fix the leak without removing the steering box.

Looking at your first picture, I see seepage from the joint between the main steering box case and the pitman arm shaft lower bearing carrier. That's all I see though so it could be coming from somewhere else. But it looks just like mine did :/

The experts say you shouldn't separate the pitman arm from this type of steering box since it's a precision fit. MB doesn't sell separately a pitman arm for the 124. The FSM procedure for working on the steering box calls for precise measurement of the gap between the steering box and the pitman arm along the pitman arm shaft so the pitman arm can go back exactly the same way. I don't get it since the rest of the steering linkage can't be built to exacting tolerances for what they cost. Point is, the FSM shows you how to remove and install the pitman arm so you can get to the seals.

And make sure it's not windshield washer fluid dribbling from the reservoir if the reservoir sits over the steering box. The ACC auxiliary pump might be in that area as well.

Sixto
87 300D