My KaBar is about 24 years old now, every three or four years I rub in a good coat of Sno Seal and heat it up in front of a hair dryer to let the paste soak in. Works perfectly. Did the same with the smaller version I picked up a while back.
Lexol would do, too.
I personally wouldn't want to put any kind of hard finish or sealer on the leather, but that's just me.
Denis