I suspect the saddle was over-treated, degrading the leather. I have Brooks saddles older than that still holding up fine. My commuter has a 1972 B-66, and my fixed gear has a 1967 Professional and gets regularly ridden on 40-100 mile rides.

While Lexol and mink oil may be fine for treating 100 year old horse saddles, keep in mind that horse saddles don't suspend your body weight between two fixed ends. Bike saddles need to retain strength to support your body over the saddle frame, and this means different leather treatment to preserve that strength.