W124 Steering too much heavy

[presscot]

My 1994 W124 E 220 got the problem on the steering system.

The steering is too much heavy and slowly return back to the center when turning left or right.

What I've done are here :
- I've changed the power fluid and replaced the filter.
- I've overhauled the steering box.
- I've changed all drag links, joints, everything about steering system.
- I've done correctly on wheel alignment.

But there still too much weight on the steering. Then, I went back to my technician and he had a new adjustment on the steering box but the problem still remains...

Now I'm very tired every time I drive this car.

What to do next, please ? please help me.

Thank you