I was just wondering what the result of this would be? assuming the Cpu is cooled by a separate block and the oil is left at ambient temperature. The oil should not really cool down much so no problems with condensation and if you insulate the lines from the cpu block it should not cause water ingress. You could even seal the oil bath to prevent water getting in. Even if it did it should separate out I would have thought when you shut the system off.
Would be a fun and fairly easy experiment to try