I use mink oil on my sporran about once every other year. It does darken the leather, so spot check it first. It waterproofs the leather. To keep my kilt straps nice, and my sporran/shoes/boots/wife's purses/leather couch/shoulder bag/all other leather products, I use this:

https://www.amazon.com/gp/product/B0...WOC2D6EV&psc=1

I understand that Skidmore makes a water repellant version now, but I haven't tried it.