It depends of course on who made the holster and mag carrier, but most often, top leather and saddle makers used to use extra virgin olive oil on newly made items and then put them in the sun to get that light tan/brown color that looks like a natural finish. I would suggest that you go down to a leather shop like Tandy and get some leather solvent that is used to take the shiney finish off prior to redying and apply liberally. Then after it drys give it a good going over with saddle soap before trying your coffee or baking soda treatment. If it's olive oil that has gone bad the solvent and soap should suck it out of the leather.