I make my own leather conditioner, I don't focus on waterproofing completely but conditioning and protecting. I do leather work that I sell, leashes and collars and have been working on perfecting recipes to sell along with the leather items. So with that, I won't give away any recipes lol. But I recommend playing with:
Beeswax and lanolin for protecting/sealing leather. For conditioning and restoring leather avocado, olive, and neatsfoot are some classics. I'd look into ingredients of high quality lederbalsam. I come from an equestrian background, and we put out leather through the ringer lol. So I treat all my leather the same way I did with expensive saddles, bridles, and riding boots because quality leather will last a lifetime if taken care of.
The best for leather is to do each step individually, as opposed to all in one type products. Of course all in one saves time. I use homemade soaps to clean my leather. It should be allowed to dry after cleaning before conditioning so you don't encourage mold growth. Best is to oil in light layers, allowing each layer to soak in completely before adding another. If you're restoring leather, this can take a LOT of layers. Caring for already good condition leather may just take one or two after cleaning. Wipe off any oil on the outside that hasn't soaked in, and apply a more sealing product if you're using that in an additional step. Leave to soak in, and buff the leather before use.
In reality you can use pretty much any oil for leather, and using any oil would be better than no oil at all. Leather breaks down because it loses the natural oils/fats inside and then the stiff fibers break down. I have a pair of high quality leather boots I bought in 2004 and wore almost daily for a couple years that still look like they were only just broken in. And I still have my first pair of show boots going back 20 years. They could still be cleaned up and worn in a show and no one would know the age.
