Probably one of the best treatments for old leather is "Blackrock Leather "N" Rich" that comes in a small jar, and is used like a soft wax rubbed into the entire surface of the old leather . It softens the leather and dramatically reduces brittleness and future cracking. It does not heal leather damage that has already occurred. It does darken the leather somewhat after application, but for its preservation benefits, that's a small price to pay. If applied correctly, when done, it allows you to handle old leather pieces, including hunting bags, without the fear of having them break in your hands. I have also heard that "mink oil" is good for old leather, but have not seen or used it myself so cannot comment on its effectiveness.
Shelby Gallien