Could indeed be alignment, but...

How much free play in the steering before the wheels start to turn?

With the car off (steering column unlocked), stand outside with window open, and see how far you can turn the steering wheel back and forth before the wheels react.

Problems here could cause the symptoms you describe. You have replaced every other suspect on the front end.

I have found that most high mileage 124s can benefit significantly from a steering box adjustment to take up play in the box.
This can really improve straight-line center feel, particularly over rough surfaces, and in the wind.

I have also read that the steering coupler on the steering shaft can cause excess play, but have not yet observed that particular problem.

Best of luck.

__________________
1986 300E 5-Speed 240k mi.