sand sealer over the oil soaked wood. I have a tower trainer that had a leaky fuel tank and it flooded the entire bottom of the plane. Stripped the covering. Let it dry out. Sanded out the warps and puttied it up. Several coats of sand sealer. Recover with monokote. Just watch the heat because the sand sealer can off gas causing bubbles. You can try titebond as well but when I tried it out, it actually melted/bubbled off from the heat of a covering iron.