I have used toilet wax for years. It doesn't seem to degrade the leather.
I put my boots in the oven on foil at a very low setting. (no gal at home to complain about it) it is around 120 deg. I warm up the boots and using plastic gloves, work the wax into the boots. Doing this several times allowing the wax to work into the boot until no more wax melts in.
Toilet wax is sticky stuff and picks up dirt and dust. They get really stiff in cold weather, and in hot temperatures they will get soft and melt. You won't be wearing your boots for church, that's for sure, but they will not leak.