I respectfully disagree with my friends who advocate the use of Neatsfoot oil.
:shock:
That is for use on leather that must be lubricated in order to flex, such as harness, drive belts, maybe baseball gloves. It will eventually cause rot and hardening.
I want my belts and holsters to remain stiff!
Although I have used whale oil (it does not harden or go rancid) mostly, I keep my leather air-dried, and wax exposed surfaces.