oils that are best on leather are water-soluble ones for the reason that leather is waterproof anyway. It can get soaking wet; just let it dry out. What you don't want is for leather to be totally dried out. For many folks just the sweaty oils from sitting on their Brooks keeps the leather conditioned enough.
I've learned a bit about leather lore being a civil war reenactor. A lot of leather was used back then. Much knowledge has been forgotten.