RE: OIL ON BALSA
Yea, oil is tough to get out.
Several applications of K2R may be needed. You can also try several applications of alcohol followed by cornstarch or baking powder. You may even want to let it sit in the cornstarch/baking powder overnight.
Once you have gotten as much out as you can, then a layer of paint, or Balsarite will help to keep the oil away from the surface.