I usually don't like resurrecting old topics, but this one I feel is important.
I work in service engineering for a large bearing manufacturer that sells lubricants. I'm also a director of the Portland, Oregon chapter of the Society of Tribologists and Lubrication Engineers (STLE).
If straight mineral oil were a good lubricant, then it would be sold as a lubricant for all sliding contact surfaces, but it is not suggested for sliding or rolling contact surfaces, especially when water or other liquids are involved. You should not replace a "food safe" grease or oil with petroleum (made from fossil oils) or mineral oil.
There are three types of food safe lubricants available. H1, H2 and H3. Most food safe lubricants have additive packages that allow them to work better than straight mineral oil. Mineral Oil is easily washed away where water is present. Additives to the mineral oil base and thickener package will allow the mineral base oil to stay where it is needed when water is present.
Attached is a link that you might find useful. This should be especially helpful to those of you that have motors and pumps on your brewing systems.
http://www.machinerylubrication.com/Read/1857/food-grade-lubricants-basics