I'l toss in my 2 centavos. Why not? Opinions are cheap.
This sentence is the key, to me:

"The saddle lived in southern California heat its whole life and was neglected just like the bike."

I think that once the leather has dried out to a certain point, it's pretty much dead. No amount of oiling will resurrect it. I think what it has lost over so many years of neglect is not its natural oils, but those are oxidized and gone too, but moisture content.

As I remember, Tony Colegrave, the man who contracted Brooks' repair and recovering service for many years, has "re-hydrated" some old leather saddles to a point where they don't tear apart.