I have given up tending a brooks saddle other than putting a bag over it when I park it outside when rain is possible. But the top needs no treatment, it is protected by my butt or plastic bag, the bottom needs no treatment, it is protected by the fender and the toolbag plus plastic bag stuffed under it when moving.

This might be different in an arid environment, but I actually live in a pretty arid environment 3 months out of the year anyway and the leather does not degrade across 10s of thousands of miles.