Does the PS pump make noise when you turn the wheel against the steering stops? ( the nose is from the pressure relief. )

MB steering gears don't use a torsion bar / rotary valve that is relatively tolerant to dirt, they use a valve and reaction ring. I haven't gone through exactly how these systems operate.

I'm not sure if your box is the same, but have a look on the 124 performance web site and here How to reseal a MB steering gear for what is inside a 126 steering box . The top pic shows where the valve is and step 8 shows it's removal.

I wonder if you didn't get a big chunk of dirt in the line and the valve is jammed.