I worked on a mink range for 3 years in high school. Don't use the mink oil. It will help waterproof the holster, but it will also
soften the leather to the point it won't hold it's shape. It will also darken the leather if it not dyed, and can change the color if it is.
shamster is right. Use polish on the outside, and the inside IF it is smooth. Otherwise just leave the inside alone.