Actually if it slides grease if it rotates oil doesn't really hold up that great. In a machine shop every lathe,boring, milling machine, slides you don't grease the slides you oil them. Wheel bearings rotate you grease them diffs rotate you oil them. A mobile crane extending the boom slides and you grease the contact points. So there are different variables that come into it. As long as it has a suitable lube there is no problem. If grease works then fine but oil works just as good in this application.