also if you did have a sealed case, since hot air rises, so would oil, so if you made a very tall case, the warm oil would go to the top, cool and go back to the components(convection). The only thing that concerns me is the cpu. It said on Toms hardware guide, that you have to seal the CPU bay.
EDIT: I just thought on how you would get a fan to circulate oil is to take off some of the fins so it would look something like this(I did this in MS paint real fast)
