Teflon, brass, bronze etc. would all work in place of the steel. Teflon would not need any grease, although the rear part on which the rack teeth slide would still need greasing but I suspect that many users would not grease anywhere.
Teflon could be adjusted to be a bit of a tighter fit but teflon flows or creeps and I suspect that over time it would flow away in the region of the screw pressure and hence loosen that initial tighter fit. Maybe a thinner piece of teflon backed up with a steel plate would work well. On a practical side, my scrap box had a few pieces of steel plate but no teflon.
I have a funny story about that. Back in the 1960s I built a rotary disc inlet valve 2 stroke engine. I had just heard about this wonder material "TEFLON" and I thought that it would be the ideal material for the valve because of its low friction. I realised that it might grow due to centrifugal effects at high RPM so I inserted what amounted to a small knife in the lower part of the housing to trim the teflon to the size that it wanted to be. It worked too well. The teflon grew and the knife trimmed it, then the teflon grew and the knife trimmed it, then the teflon grew and the knife trimmed it.......................
I then replaced the teflon with thin steel, hard chromed. That worked well. Here is a pic of the steel version, I have none of the teflon.
Attachment 42209 Click image for full size.
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