As a Fifer in an American Civil War Reenactment unit, I have been in the habit of keeping my Sweetheart blackwood Bb fife well oiled, and rubbing it in as I would do with a musket stock. It just seems to play better if the wood is impregnated with oil, IMHO.
I once bought an 1864 CLOOSE “C” fife at a pawn shop that would not play at all - come to find out it had a hairline grain seperation / split / crack along the bottom that i could hardly see, but which rendered the fife essentially mute. It would make noise, but no music.
Did I break out the glue - pot? NO!! But after a good oiling and some time, the parched wood expanded back to it’s original volume, the split closed up, and the fife played again as I imagine it might have back in 1864.
As the natural resins in the wood which fill out the spaces between the cellulite structures evaporate (they are somewhat volitile) the wood tends to contract, or shrink. This is why “wooden indians” and chainsaw art usually splits in several places as it drys out.
We don’t want that happening with our flutes, now do we?
I have slathered oil onto the inside of old guitar decks that have split, and you can just about see the wood expand and the splits close up.
Needless to say, I’m becoming a big fan of oil finishing on guitars as well as flutes and fifes.
Oil at least partially replaces the lost resins, helping the wood to maintain it’s volume and prevent splitting. I think it also contributes to the density of the material, and thus it’s harmonic resonance.
Oil impregnated wood seems to be a more efficient conductor of sound than dry wood with it’s multitude of air-filled chambers among the cellulite matrix.
Some of you here would pitch a fit if you saw the way I utterly SLATHER the oil (I used to use peanut oil, but found that it went rancid after a while and smelled nasty, so now I use toasted sesame seed oil. Works for me) to my wooden instruments.
As a general rule, if the surface looks dull and feels dry, I’ll pour a nip of oil into the ambrochure, tip the flute up so it runs down to the end (and all to often dribbles on to the carpet - gotta quit doing that), run a .410 (for the fife - 28 guage for the flute) shotgun mop-swab up the bore with a length of shotgun cleaning rod while twirling it around a bit, then rub whatever slobbers out the holes into the exterior until it glistens.
Sometimes I take a Q-tip to make sure that the end grains around the edges of the holes get a good dose as well.
I’ve been using this technique on my low “G” black walnut flute “Gilead”

for years now, and the slipprier she is, the sweeter she sounds.