How can I remove an oily stain from raw wood before painting?
Mix a box of baking soda or sawdust with mineral spirits or isopropyl alcohol to the consistency of toothpaste and rub it in with a soft brush, leave for an hour and then hose off.   Preheating the wood with a hair drier or as if in the sun to allow oil to flow easier , then reapply ,  If the stain persists repeat.