occasional stiff steering - pump or rack?

I'm wondering if it's the problem with the PS pump or the Y10 solenoid?
The steering was extremely stiff at idle and really low rpms but once the rpm increases everything is back to normal. Made parking the car or just general low speed manoeuvres a nightmare.

As the assistant is turning the wheel monitor the reservoir for any air escaping and ensure the fluid stays at a pretty good level. You do not want the pump to draw any air as this will be very difficult to remove.
If all checks out let me know and then you can proceed to the next step in finding the problem.
Last edited by taleb659; Sep 14, 2014 at 06:25 PM.
Checked Steering fluid level. Found it low. Purchased and added Steering Fluid from MB dealership. Drove about 20 miles. Turned a dozen times lock-to-lock left and right. Fluid level stayed good. No improvement.
Some background: This car had a leaky Steering Reservoir "O" Ring. Reservoir was replaced at MB dealership about 9 months ago. Was and still is no longer leaking. Not sure why level dropped at all.
I will try the 30 turns while jacked this weekend as suggested by previous post by taleb659.
In the meantime, any other suggestions to bleed any air that may have gotten in to the system?
Thank you
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