Having read a post on using Meths I thought that I would post this from my experiences. Appologies for duplication of my comments in that post. click here
A proven tip for cleaning toner deposits from printer and fax drums (OPC, Organic Photo Conductors, selenium and CDS Cadmium Disulphide) is a drop of spit and some of the same toner, applied very lightly, in a circular motion (a discoloured patch may remain for some time until the drum has healed). Also be very careful when cleaning the mirrors in copiers etc, as they are FRONT silvered. This means that they are opposite to the mirror in the bathroom etc. They are FRONT silvered so that light is not distorted by having to pass through a layer of glass first. If in doubt contact the professionals.
A recurring spot/blemish always in the same place on the printout/copy paper is usually a mark on the glass of the copier or scanner. A wandering spot/blemish is usually a mark on the drum or fuser roller/sheet. Similarly a line through a fax can be a mark on the optics because the original passes under a static optical display.