Like most firearm owners, my leather holster collection has grown over the years. I store most of them in a nylon bag to protect them. What products would be useful in preserving/protecting them? I notice some of my older natural colored holsters are darkening with age. Is this normal? Should it be prevented? Is this an indication of the leather holding moisture? Also, how can I prevent that green stuff arould the brass hardware from forming? I assume its corrosion of some sort. Some holsters have it while others dont. Can this "green" also be prevented?