Oil and religion.
The former would be a non-hardening oil, since a hardening oil would block all but surface coat applications and they are far from tolerant of water.
The latter would be with regard to maintenance. The more religious you are early on, the better the results you will get.
I built a garage door from leavings I picked up from a cedar mill spalt pile. I applied a coat of used motor oil thinned about twenty percent. Within a month, you could hardly tell I’d done anything. The second coat reacted similarly. The third, however, was notable several years later. In short, the oil coats are cumulative. Rather than evaporate off, the oil wicks in and more can be added.
If a chunk of wood is saturated with oil, water isn’t going to penetrate it. Saturated with oil, it’s not going to dry as quickly, so will be far less to shrinking and cracking. It will remain resilient, rather than brittle, like cedar shakes and shingles get in the hot summer sun [but wouldn’t, if they were well oiled].
Oil will even swell old, dried wood and hide much of the splitting and cracking.
My preference would be to thin the oil about thirty percent. Ideally, it would be with turpentine, but paint thinner will do.
Now, on to my latest experiments.