Like mentioned, Over boiling the leather will end up making the leather briitle. What i use to restore ( over statment ) but what has worked wonders with either very old, ill treated/etc. leather products is Gun Oil, the one that has Teflon, even gives it a nice shine. ( leather will be come soft for some time) i tend to use q-tips and apply fast coats, the leather will soak upo the oil at different speeds on differnet areas, i apply small multiple quantaties layer. The leather will redistribute the gun oil over time ( days) so stuffing pouches, or having the buckles and lace conected so that the item maitains or keeps the right shape. One other secret is to place the oil and the leather product in the sun for 20-40 minutes, this wil help the oil penetrate the leather.
Once again use small amounts of oil and work up quantaties, and do this in 2-3 periods in a 24-48 hour period, it is possible to over oil and that will take a long time forr the exses to be removed.
Hope this helps, i was able to restore a old pocket knife sheath that was over 70 years old and looks great.