W126 steering lock problem

On my almost 91 W126 300SE, after making a turn requiring a full lock on the steering, the steering does not automatically return to neutral straight ahead position when I proceed.

I just had the wheels aligned, and my mechanic has tried make some adjustments to the steering block (?), but to no avail.

As this is a relatively minor irritation, I just turn the wheel back to straight ahead, do I need to get this fixed? Will it cause safety problems or will the repair bill be much larger if I don't get it done?

I have owned this car for more than 4 years, but never once did it exhibit this problem before.

thanks.