My X2 clone, actually a Warco MiniMill came with corrugated plastic covers for the Y axis. (Is that right? I'm referring to the forward & backwards slide as distinct from the side to side slide.) These quite quickly cracked and split in the folds of the corrugations. I then replaced them with other corrugated plastic stuff supposedly meant for this job but which also quickly cracked and split. In the end, I used an idea by, I think, Harold Hall and that was to use polyurethane varnished cardboard from breakfast cereal packs, lightly scored where I wanted folds. These are lasting much longer than the plastic stuff. The downside is that they are stiff and get in the way when up against the travel limits, mainly up against the column. Hence, as I approach the column, I use a slim rod, screwdriver, whatever just to lift the cardboard such that it then bunches up above the slide.
FWIW, I used two coats of any old indoor coloured varnish, just what was left in the bottom of the can.
Peter G. Shaw