asmac, a horse saddle is supported underneath by the horse, a bike leather seat is hanging between a metal frame, so if you soften it too much, it will sag.
Reread the letter sent to me describing this, specifically about not wanting the seat to "bow".
I believe the prob with oils is that they break down the leather in a way that you dont want in an unsupported leather seat, like I said, on a horse its a diff thing.

also, in the letter the guy says to put some proofide on every 500miles, I certainly dont do that. I put a bit on once a year maybe, so this year Ive put about 3000km or 2000 miles on one of my Brooks, and it doesnt look or feel like it needs any. I will prob put a smidge on it after it sits in a dry house all winter, but thats about it. So in other words the small can of proofide I bought with the seat will last me many many years, the price of a fancy beer in a restaurant, so why not just use proofide that Brooks figures is best for their seats.

or not, its your seat.