The online community of knife collectors, A Knife Family Forged in Steel
When leather reaches a certain point there's not much you can do but enjoy what it's become. I've seen a lot of them hardened out like that, usually because some well meaning individual oiled the leather with the wrong oils. Machine and other petroleum based oils are bad for leather and will make them hard and brittle. Leather is organic and does best with animal fat oils such as lanolin. Some vegetable oils work well depending on how the leather was tanned/processed originally. There are synthetics out there that work, but sounds like someone used the wrong oil early on with your Kabar. Knew a lot of veterans that treated their's with motor oil as it was all they had available - big NO for the leather.