Tom,
I had a similar issue with my MicroMark 7x16. I had two issues contributing to the poor mesh of the rack and pinion gear. (1) I moved the rack down for a better fit as others have done. (2) The pinion gear was bad fit in the hole in the apron. I took the apron off and bored out the pinion gear hole and turned up an oilite bushing to fit the bored out hole. This removed the sloppy fit between gear shaft and ?apron bore. This made a dramatic improvement to the rack pinion mesh. The sloppy feel is gone.
OldToolmaker