There are lots of recipes online for a beeswax , turpentine, mineral spirits mixture for waterproofing. I haven't used that on leather, but it should work- it works on canvas well. I have used a mix of neatsfoot oil & beeswax. I mix it about 2:1 oil to wax by weight. I'll tune it by adding more of either if the consistency doesn't come out the way I want. By adjusting the proportions, you can get it to a thick lotion / cream consistency with more oil, or a harder paste with more wax. I've toyed with the idea of adding shea butter or cocoa butter to smooth out the texture.
It will darken the leather. If you use a heat gun / hair dryer to help it soak in, the leather darkens even more.
I'm not sure about longevity. I haven't been doing it long enough to tell for sure.
The recipe for Fiebings Aussie leather conditioner is Wax, Mineral Spirits and Petroleum Jelly acording to the MSDS. 10-15%, 15-35%, and 55-70% respectively.