Yep, sintered bronze bushings absorb oil through osmosis. It's fairly high speed so I wouldn't go thicker than 30 wt. If you drip a drop or two of light oil on the outside of a sintered bronze bearing you'll notice the absorption action before long. I've seen guys cut scroll grooves in them on the drilled ones on cam bearings but you want to have a good stream of oil feeding them. If you didn't think it was getting enough oil you could drill a tiny hole through and use a dremel to cut a blind scroll groove that stopped before the edges of the bearing. Scroll grooves are usually X shaped across the hole or spiral shaped.
I looked into making my own but decided not to after I read you have to have the sharpest smoothest cutting action to cut sintered bronze as the pores can be blocked from too dull a tool. I'm not sure the best way to clean them other than a solvent bath or maybe boiling them??? You can't use crocus cloth, hones etc as that will plug the pores. I'd just make sure the shafts are smooth with no burrs and call it good.
