Linda;

When the leather reaches that point where it's condition has deteriorated to "crazing" or actually cracking/splitting at the surface, there is little remedy. Healthy living tissue will heal after being lacerated, but tanned dead tissue cannot of course.

I agree that your vintage holster belongs with the Colt. Despite any condition issues. Use whichever of the suggested preservatives that have been mentioned. Most of them will achieve the same results to preserve and stabilize, which is the best outcome you might expect. Feibings Bag Kote (neutral) will seal and polish the topcoat. It can be dilluted with water to achieve the desired results. A word of caution, areas where the top finish is totally worn or gone may darken with the application of any of these products. So test a small spot first if possible and be conservative. As usual, great photos!