Welcome aboard,
I use leather holsters also with very RARE exception. When I get a new one I use Atsko Sno Seal on it. Its basically bees wax, it preserves and waterproofs. It will darken leather slightly. If you have not used it, put the leather on a sunny windowsill until warm and then just start rubbing it in. After wipe it good until its not sticky and your done.
Also use it on slings, boots, and I even did a 20 year old dried out bomber jacket.