I’d like to pass on some hard-earned info. to other X300 owners.
My '95 XJR6 had occasionally lumpy & heavy power steering which seemed worst at low speed turns, which I lived with for a while but eventually I realised it was not going to fix itself.
I scanned the archives for clues - first possible cause was identified as the Servotronic steering controller or its wiring.
So I cleaned the connector on the rack - no improvement, changed the controller in the passenger footwell - no joy.
Next traced all the wiring, no problems found, bypassed it just in case - no improvement.
OK, time to get serious - a used steering pump from a friends spares stock, known to be good, was fitted. No improvement.
Then the rack itself was changed for a good used item. Still no change.
Working on the basis that there was not much left of the original steering mechanism, so the reservoir (with internal filter) might be blocked - swapped that for another. Nope.
After each of these changes, the car was test driven and each time I managed to convince myself that the problem might be gone. The longer the test drive, the better it felt, but each time I left it overnight and drove it again the next day it was clear there was no improvement.
In the end I had changed the entire hydraulic system except the pipes, and the electrical controller, and still no improvement! Time for some lateral thinking.
The worst thing about the problem was the lack of self-centering when straightening up after a sharp turn, it felt positively dangerous. Also the steering was not just heavy, it felt notchy in both directions.
The only moving parts not yet changed were the ball joints and the steering column.
Notchy, steering column, UJs? - some light oil on the steering UJ and bingo! Fixed. What a difference!
If only I had tried that first. Yes I am an idiot, the clues were there all along.
The moral of the story - take a step back and consider the easy stuff first, don’t assume the worst and think about the system as a whole before diving in and changing stuff!