I have a French Brooks type leather saddle from the 1930s. It was rock hard and deformed. The London Museum has a web site for restoring archeological leather. I tried one of their methods which was a glycerin soak. Saddle soap is a glycerin soap so I thought I would try it. They recommended mixing the glycerin with acetone or ethanol. Alcohol is not as good as it dissolves some of the tanning chemicals. I did it in the bathroom so I didn't want acetone fumes in the house so I used 99% isopropyl alcohol. I used a pint of alcohol and 8 ounces of glycerin and only let the saddle soak for 8 hours to avoid removing the tanning chemicals. While soaking I used a large close pin clamp to move the sides of the leather to the saddle rails. I used a pan made out of aluminum foil for the soaking. After it dried for a day I soaked it in neatsfoot oil for 3 days in the aluminum foil pan, keeping the clamp on. I would rotate the saddle in the pool of oil so all areas got soaked. It is now flexible, but hard like a broken in saddle. Now I am using Kiwi leather restorer, which is a much softer paste than Mink Oil. I think Mink Oil or Snow Seal would also work. I put on a thick coat of this every 2 days and it magically disappears into the leather.