FWIW I will throw in bit of useless info after reading about using motor oil and such on handles. In my limited experience(I am definitely not an expert/knowledgeable here, take what I say with a "grain of salt"). Seed oils like flax seed oils or any naturally based oils work better. BLO, raw linseed oil, Danish, Teak, Watco or whatever work better on wood. Raw linseed oil has become my favorite. Thin, forgiving and easy to use. Really, really easy to use. Wood seems to last a long time if kept oiled with these.
Petroleum based oils(motor oils, hydraulic fluid and such) seem to cause the wood to rot with time if any exposure to the outside. Much better results outside with something like "Thompson's Seal Weather Proofing treatment" here.
It might take two, three, four or six years, whatever. The petroleum oils seem to cause the wood to rot and break down with time. May be different if stored indoors. IDK. I was using used hydraulic oil from tractors and a mini-ex for several outdoor items(trailer beds, home-fabbed benches and big 6'-8' wooden spools used as benches/work tables). It was free, available and on hand in 5 gallon pails after oil changes. And I used it a lot, very regularly. The untreated wood(spools) failed first, maybe three years?. The treated wood on trailer beds is doing better but still rotting. I have had a change of heart using petroleum based oils on weather exposed outside wooden items. The wood will rot. Your handle, your choice. Just a bit of my very limited experience given.
And YES I have read about using diesel fuel, throwing the axe in the creek and such. To each his own. My first choice is a flax seed oil of some type as a preservative for handles. Applied liberally and regularly from the start. Wooden handles seems to last a long time if not busted/broken given such treatment. Again, just FWIW