Well, Pete, ye of little faith, it works! This is a test 'pot' about 45mm diameter of ash, cut across the grain (from a small offcut). I have filled it with the oil fluid from a sticks-in-pot scent diffuser we had, and as you see the oil oozes through and it scents beautifully. It also forms droplets on the outside which is perhaps less ideal although the remaining chuck point/foot on the base has so far stopped these reaching the surface.
The interior is simply drilled out using a 35mm Forstner bit most of the way down, with no further finishing, leaving walls 5-6mm thick, and the exterior is sanded but then wire brushed to open the grain (of course no other finish). The lid is a reasonably tight fit - I could say it is cut on the end grain because that then lines up the pores correctly but honesty compels me to admit that this was an accidental consequence of the shape of the original offcut!
So an improved design might have thicker walls to slow leakage, or perhaps be made of a less open wood, with some form of deliberate drop barrier at the base.