I don't own a layout, but I'll repeat that based on my friend's experience denatured alcohol works well as a track cleaning fluid in the CMX machine. Never had any compatibility issue or rolling stock or scenery damage. Of course he is careful not to handle rolling stock if his fingers have alcohol on them.
His track cleaning train consists of one of those cars with a slightly abrasive Cratex rubber roller, the CMX car (bought when they were much less expensive), and the Centerline cr with a dry soft roller to dry the track.
I'm not a chemist, but in my experience fluids like Naphtha work better than alcohols when used as degreasers. That brings another one of "those" questions: what exactly is the composition of the gunk that accumulates on the wheel treads and railhead. I seem to recall that back on the Atlas forum someone wanted to use a chromatograph to analyze the composition of the model RR gunk.