Neatsfoot is pretty good with cowhide and finished leathers, but you have to watch it on the thread since you evidently have an antique.
IN another post somewhere I posted this formula for Dubbin;
1 part liquid lanolin and 1 part rendered beef or mutton tallow. The former will come out of a healthfood store. The latter can be made from trimmed fat rendered at a heat low enough to prevent sizzling or smoke.
Add about a 1/4 part pine oil.
The first time I did this, at the advice of another Cordwainer, I thought I goofed because it came out like jelly.
The beeswax mixture mentioned above is alright, but beeswax will tend to stiffen and run out in weather. Even so the MIneral Oil will tend to hang around.
Dubbin goes back to the middle ages. Regretably, we can't get Sperm Whale Oil.
You also have to be careful to make sure that this is an antique. Some of the craftsmen out there will induce an artificial aging effect by using chemicals such as oven cleaner or paint products to beat the snot out of the leather surface. I never did that, but neither have I ever seen someone's bag treated as such fall off their shoulder from rot while still looking soooo goooodddd...
In that event, rub whatever you are going to use in a small patch of hard-to-see leather on the bag. Let it sit for about a day before doing the whole bag.
Don't shoot yore eye out, kid
The Capgun Kid
AKA The Still River Cordwainer