A little bit of input I can give you...
The rack in my car had a split boot and all the oil had leaked out long ago. Not knowing any better, it was driven like that for some time. I took it out while doing an engine refresh, and found that the shoe was very worn (no surprise there, with no oil!) to the point that it didn't have any spring tension on it. That explained why the rack was so sloppy. I re-shimmed everything and had to make a spacer for the shoe to get the right tension, and put on new boots and oil.
Before I put the oil in, and even after, it had what you could describe as "lumpiness"; a kind of stick-slip friction that kept it from being smooth. Once in the car it was fine-- the level of forces on the rack when actually steering the car are much greater than the friction, so you don't get that stick-slip. Even with the wheels off the ground, you cant feel it at the wheel because of the leverage. Remember that you are dealing with a metal-on-metal shoe, and it doesn't have any lube when it's apart.
For oil I used Pennzoil Syncromesh. It is compatible with yellow metals (bronze, brass, copper). I also used it in the trans, and have been using it in other transmissions (T5's Tremecs, etc.) for years with good results.