If you are going to use it, the poor soul needs a kind drink of leather treatment. You can use Brooks Porfide or some swear to Pecards Antique leather treatment.
Whatever you treat it with, take it slow and do not put to much on at anyone time. I would be tempted to start with Pecards as it comes highly rated for old leather on the military forums. But you do not want to make the leather, it needs lubrication in the fibers.
Even so, the leather might be to far gone and crack tear through the rivets anyway.