you should always protect the wood, some solvents can soften and rot wood. some woods are more vulnerable to rot from solvents and oils. that why walnut is the prefered wood for rifle stocks along with a few woods from northern europe. Many woods have the very desirable strength and stability characteristics that make them ideal for stocks but they rot away and soften when exposed to solvents and oils. Walnut is unique in that it does not rot away like that.