Neatsfoot Oil?
The good folks at rivendell advise against using too much of any leather conditioner on brooks saddles - you can break down the leather and make it too soft.
I too, had an Ideale for years until one of the rails broke- i replaced it with a Brooks and have never been happier with a saddle. I haven't treated it with anything yet, just ridden it a lot.
I would be extremely cautious about ruining my investment in my brooks saddle by using too much neatsfoot oil!