Oil makes a bit of sense in the top nipple, simply because the drilling is tiny, and emerges above the upper bush. But oil will be more likely to drain away sooner, and some types of hypoy gear oil can affect bronze bushes. I think to change from grease to oil may not provide any benefit, simply because the grease already there will stop the oil penetrating between the upper bush & pin.
So if you fancy trying oil in the upper nipple, the time to do it is after a rebuild.
