Hello everyone

My 'new' Buick has an annoying problem with the power steering and I am not sure where to look first. It is a 1981 X-Body Skylark. Take a look at the video:

https://youtu.be/DhVx_soZD8k

When starting the car and its dead cold you have no steering assist at all when turning right. After a few seconds it kind of works but only with a nasty vibration which is even visible in the mirrors.
The fluid seems ok, but I haven't changed it so far. I topped it off to ensure it hasn't some air trapped inside the system.
When I lift the front wheels off the ground turning the wheel to the right is harder than to the left but that vibration noise doesn't occur.
I don't think its the power steering pump because steering to the left works just fine. But I might obviously be wrong.

Thanks very much
Flero