Putt:

Pull the engine, the mount, and anything else that is on the firewall.

Use rubbing alcohol as a scrub with a scrap cloth, clean it as well as you can.

Then, if you can find K2R spot remover, repeat its application until you don't see any difference between applications.

The Eco-Nazis have been hemorrhaging about K2R, you may not be able to find it.

If you can't get K2R make a sloppy paste of cornstarch and rubbing alcohol, smear it on the firewall and let it dry. Repeat application until you see no difference before and after.

All this is to pull the oil out of the wood.

Once the oil is out, or as much as you can get, paint it with thinned epoxy, thin ca, or any fuel proof paint.

And hope you did it soon enough.

The oil will turn the wood into a gooey mass.

Bill.