I just read that the rack and pinion steering box for the XK8 is of a variable ratio design. "As the steering is turned, the conventional pinion meshes with the rack teeth whose angle and spacing progressively increases, lowering the ratio and making the steering more direct."

Are all rack and pinion replacement units like this? I may have to get a replacement.

I see a lot of refurbished steering racks ranging from $300USD to $1,750USD. There must be a difference between them.

For ex. From BuyAutoParts for $315 and then from Gaudin Jaguar for $1,279

 

The difference is the cheap on is remanufactured and the expensive one is likely new (or the price was based on the price of a new one and not the re-manufacturing cost or the current market).

If the rack isn't leaky, but is just sloppy, replace the inner tie rods. That did wonders for my car, for less than $100.