I made the suggestion because that's how General Radio did their reference capacitors and it's a very clean way to do things. Oil has its own set of problems, though the probability of success is high. I don't know how foil resistors are bonded, nor if oil will have any long term effect on them. Look up what people worry about with the classic L&N resistors. Oil can become acidic and should be changed periodically. It will, of course, help your power handling immensely.