Technically, I believe Sheldon's site only recommends soaking for the extra thick leather saddles, like the Brooks Professional. Otherwise he recommends the "pour and rub" technique.

As BluesDawg states, there are a lot of pro-Brooks cyclists who do not agree with Sheldon on his heavy use of oils. And, it should be noted, that Brooks disagrees too.

I've read reports by people here on BF where they have ruined Brooks saddles by using too much oil / proofhide.

I don't own a Brooks, but if I had your B17 and it was already oil soaked, I would be very careful with it. I'd try to find a way to get some of that oil out.