I received some old PCs from a business. Most of the parts are old and only good for proper recycling. The CPUs are interesting, however. Most look as shiny as they would have when they were new, but a few had tarnish on the back. What I mean by this is that a few of the gold/copper pads on the rear of the CPU look like old brass when it needs some Brasso polish. Is this a bad sign or merely normal for CPUs which have been handled by oily fingers? Is there any way to clean them, for example, some solvent on a q-tip?