When the weather is very hot an oily substance comes out of the bottom of my cutout. The cutout is cold and the electrics in the house are fine. The cutout is a modern plastic one and the substance is oily, not pitch, which I know can cause this issue. My house is on a hill and the plot is the first level one for about 200 metres down from the top. I have a drive which also slopes slightly down to the house, so the cutout is lower than the pavement level. This has been happening each summer and I did ring my DNO some years ago, who didn't seem too concerned if nothing was getting hot. I was supposed to be contacted for someone to have a look, but never was. Anyway, a surveyor came round to the house last week to look at a proposed building project and we got on to where the electrics could go. When he was looking at my CU I asked him about the oil issue and he said that the oil was from the mains (part of the insulation outside) and he had seen this problem before in houses with the position that I have described above. It's gravity, apparently. Is this right?