I love the Brooks treatment threads... Having just weeded-through a bunch of old threads on this subject (on different forums as well) and finding so many different methods, I tabulated them and arrived at the most common which is neatsfoot. So,I did that..

To revive my three almost NOS 1972 & 1973 OEM Schwinn Paramount Brooks "Professionals" and a 1971 B-15, I used genuine neatsfoot oil. The three Paramount saddles had never been broken-in, but being 40-years-old, were hard as stone. (My three paramounts are very low miles, one bike is basically NOS)

I painted it on from the bottom with a brush. With the seats upside-down on newspaper. A several day process. The B-15 has a lot of miles and some weather exposure. So it had some curl and has some cracking as well, so I had it wrapped in rubber bands.

Now, the Professionals are no longer rock-hard and I look forward to Spring-time to start breaking them in. The B-15 is super nice and I have ridden some miles on it already, seems to be good.

I think it was Sheldon Brown who mentioned that in the 1970s they soaked them in motor oil, and I actually remember hearing about that method back in those days.

So, this summer, I'll know if I have ruined my saddles or not..