WD40
In my first job was in a college, my immediate predecessor was someone who believed that WD40 could fix anything... including computers. However it turns out that soaking the motherboard in WD40 does not - in fact - fix computers but he still persevered with his attempts until they got rid of him.
Also in that job, we had labs and labs of Amstrad PCs which had a light grey finish that really picked up the dirt from the rather grubby students. We didn't like these computers much, so we cleaned with with a bucket of warm water and some washing up liquid once a year. They were annoyingly resilient to this cleaning process and ended up looking sparkling.
The other problem was mouse balls.. we had to glue the belly doors close to stop the students removing the balls. However, the rollers would still clog up with body grease and skin particles (yummy) so the mice needed to be disassembled to be cleaned properly. This involved removing all the screws on the bottom, which of course would often go missing and then giving the rollers a good scrape. Thank goodness for optical mice these days..