JL:
As someone who builds custom concealment holsters in my (ha!) "spare time," (I have a small company and a website; P.M. me for details) here are a couple of tips to help that holster last a lifetime:
a) if it gets wet..remove gun, stuff it with paper towels and let it air dry. Don't set it near heat, don't put it on a window ledge (where it will remain cool, and could develop mildew) but maybe on your dresser in the bedroom. Don't put it in the laundry room: too much damp heat.
b) To spruce up your holster, use your shoe brush and brush all the dust off. Then, you might just hand rub in a bit of neutral shoe wax. This will shine it up, and will help the leather reject perspiration and other moisture.
c) If you have a rough-out holster the only thing I've found that will not typically soften the leather but WILL boost its ability to reject perspiration and moisture that could damage the finish of your pistol is a light application of spray-on silicon-based waterproofing stuff. But emphasis on LIGHT application. Rub the inside of the rig with neutral shoe wax.
NEVER...NEVER...treat a holster with: liquid shoe polish, Neatsfoot oil, any lanolin-based compound. That stuff may be great for shoes, and particularly hunting or hiking boots, but it will destroy the rigidness of your holster.