Unless I’m mistaken, the drilled cam screw that NK describes must be coupled to an upper distributor shaft that has also been drilled to allow the oil that you add to leave the shaft and flow into the bushing. This modification is one well worth making to any stock distributor other than one on a fine points car.
Even if you have this modified upper shaft and screw installed, you should also lube through the oiler to get the lower bushing as well. Use a light oil such as 3-in-1. I use TriFlow as my go-to light oil lube.
When you use the oiler, watch to make sure that the oil flows out of the little cup. I’ve seen several older distributors where the oiler or (more commonly) the passageway through the distributor body has gotten crudded up, I’m guessing from someone overzealously greasing the shaft in the past. If that happens you need to remove and disassemble the distributor, clean out the passageway, and likely replace the oiler when you reassemble.