I pulled out the little pamphlet that came with my B68, and it says, "Your Brooks saddle is guaranteed for two years from the date of purchase against defects in manufacture or materials." It goes on to say that you should return the saddle to the place of purchase, along with your proof of purchase.
You could also try
www.brooksengland.com or
info@brooksengland.com for more info.
Good luck!