97' 850 need help diagnosing steering problem

[850 LPT]

Hi guys,

When I go around fast curves the steering feels like it is binding/ jerking. Everything feels fine when I go straight and make lane changes, for example.
My first thought on this was maybe the steering coupler/ U-joint is starting to fail and binds at certain positions. I actually have a new one already which I was planning to install very soon.

The other day though I noticed something which makes me question my first thought on this: I was parked with the engine running and turned the steering wheel about 90deg to the left. All of a sudden the steering wheel started jerking back and forth. After noticing this I turned it to the left and the same thing occurred.
So now I'm thinking maybe the PS pump is starting to go and it is intermittently loosing pressure.

I guess I'm looking for your opinions before ordering a rebuilt PS pump. Is there anything else that could be at play such as the rack itself.
As far as I know the rack is original to the car, which has 250k on the clock.

Any input is appreciated.

Dirk