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Hello, this concern is caused by an issue in the steering rack. Replacing the steering rack and pinion is on way to replace it. The other is to remove and tighten the nut on the passenger side. This nut/screw is inside the steering rack once you remove the boot that protects it and the inner tie rod end.
If there is no obstruction then I would replace the power steering pressure line. This line I have also seen cause the same concern. Overtime the fluid swells the rubber and causes a restriction.
An obstruction in the power steering lines isn't possible when rubber swells. Your only option is to install a new power steering line on the pressure side.