The original quarter sawn/tiger oak door on our 1907 bungalow is in need of refinishing. The lower portion of the door has milky residue and the wood grain could be enhanced by a refinish job. I am hesitant to approach this the wrong way because this door is a real treasure. My plan is to sand it lightly to remove any lingering varnish, bring out the grain and simply revarnish with tung oil or spar varnish. Should I restain the wood? If I sand too hard will I damage/remove the grain? I can't tell if it has been stained or simply varnished. Thanks for your expert advice.