most mast manufacturers I have spoke with use a sealed bearing on the part of the mast that uses roller bearings, and they recommend NO grease in that part of the mast. all greasing will do is cause the bearing to not roll, producing a flat spot even sooner.
Also some flaking on a new mast should be considered normal, as a properly shimmed roller should not ride in the flat part of the mast, but tightly against the curved surfaces in the right angle of the "I" beam and not on the wide flat surface of the roller, but in the curved area.
Lube is recommended (usually) on the surface of what might be called a "wear strip" or "wear button" between the channels (a brass or 'oiltite' flat bearing surface).