Having the connectors exit the top (tilting case onto its 'front') seems like the way to manage leaks, especially if you ever want any additional connectors or cards.
Worse than just chemical oxidation, it seems like vegetable oil would be a viable growth medium for molds or bacteria or the like, so I'd think a mineral oil of some kind would be better. Of course, there are very few oils that can be purchased for $4/gallon like vegetable oil.
If you could get the primary heat sources (P/S, proc, etc.) to the bottom of the case, you should be able to make a hellacious lava lamp. A lot of little ones run on 20 or 30 watts, so 400 should be plenty for an 8 gallon version. Red transmission fluid with a white or dark purple parafin 'lava' would be pretty spectacular. I bet perchloroethylene is hard on plastics and might increase conductivity though...