As is the case with anything organic, aging is problematic and if unchecked, the item will become worthless and this especially true of leather. Quality of manufacture and storage conditions are major variables and I have some Civil War and earlier pieces that are in better condition than some of my WWII stuff. That owners will allow slings, holster pull and closure straps, helmet liners and natural stitching on all of the above to dry out and fall apart will always amaze me. A good example would be the original Civil War musket sling I bought as unmarked. With a little effort using mostly natural (the emulsifier evaporates) treatment when I took that musket out last, the restored moisture made the manufacturer's and inspector's stamps clearly visible. I've gotten the same results with belts, cross straps, cartridge boxes and cap pouches. To treat or not to treat is a matter of personal preference. I learned at least fifty years ago that properly conditioned, still serviceable leather sells far more quickly and at higher prices that that which has been allowed to fall apart, which I don't even buy. Getting into petty urinating contests regarding long-term leather preservation methods is a thankless task so to each his own!