do some searches for reconditioning Brooks saddles.
there are two schools of thought... leave them alone (proofhide) or carefully soak in some sort of leather conditioner. I had a B5N that came on a Dawes from the 70's. It had not been used for like 20 years. I used some leather conditioner, soaked it in aluminum foil, and it softened a bit. My daughter rides on it every day on her Fixed gear, and the saddle is dark honey brown and glossy.

As I said, do some searches and you will find a few opinions about things other than just proofhide -- which is more of a protection vs. soften/conditioning.

Some things will degrade leather... I think I even used some linseed oil, an it was fine