Be careful about following any 'brain trust' advice (including mine) received in online forums. If possible, run it by someone more knowlegable/who does it for a living (and is good
at it). I have never found any real 'expert' on any
subject (Ph.D.s included) even if they may call themselves one (that's the FIRST indicator they are not). For example, if the government really DID have economics, financial, political and foreign-policy 'experts' as they are called, we wouldn't be in these assorted messes America is in nowadays, would we.
So if you can call a local museum, ask them what they do to conserve any leather items in their collections. They would be the ones to get 'final approval' from before (if) you do anything.
I mentioned not doing anything because (1) it is not something historically original to that particular item, (2) the color might/might not change (also not original if it DID change and collectors like an items 'patina' showing its age and want that UNtouched) and (3) if properly applied (penetrating the leather completely), anhydrous lanolin (not a manmade synthetic or petroleum distallate product but completely natural -- which is good, IMO) would be almost impossible to remove later on...which for me is just fine because my leather items are not collectors pieces but used, and I want them protected from moisture and from drying out/cracking over time.
If left alone, eventually leather will dry out and crack, but if it's never used or ever meant to be used, that would okay as it's only a collector's item. Still, I would ask a museum conservator what they do. At the larger museums, they have staff trained in the care of different materials such as wood, fabric, leather and such. At smaller museum they should have at least one conservator. It's sort of like going to a library and asking for (free) help there; go to/call a museum and see if you can get any (free) advice there. Or recommend a professional 'stand-alone' conservator.
Professional conservators can help (for a fee of of course) the general public and often work with museums. Maybe an e-mail to one of them would get you free yet valuable professional advice. See this link for some info:
-- John D.
P.S. This is kind of weird: I am a RVN vet myself and we're talking about 'museum pieces' from that time period...I'm probably older than I thought.