Hello, my front exterior door is wood and was coated with polyurethane (no paint) about six years ago. It is time to refinish/protect again. A friend of mine from Germany recommends treating with raw linseed oil because he said he has seen 300 year old windows (in Germany) in GREAT condition that had been treated solely with linseed oil. I live in South Florida, so not only does the extreme humidity take a toll, but the door also faces west so has blazing sunlight on it for a good part of the day. Thoughts/advice about linseed oil or tung oil or something else in this application? Thanks.