As my time writing on this forum is now quickly coming to an end though my new word processor has cut down on the misspellings though its punctuation leaves a lot to be desired. I will list other items that will help with the restoration of leather.

For light leather colours use Glycerine soap for the initial cleaning not saddle soap, has less of a darkening effect.
For the case leather hinge line use a 50 50% mix of Cod liver oil and Neatsfoot oil, make sure that you get the real thing undiluted with other oil. This will not cure the cracking but it will prevent further deterioration.
E45 Cream works as a good leather restorer you can also add dye to this, rub it in to the leather a couple of times a week and it will restore that looked after leather glow.
For a real bad case of hard dead leather rub the leather with a mixture of neatsfoot/cod liver oil and water with a drop or two of dish soap added. Shake the bottle well before use.
Just a piece of advice Leather did not get hard and brittle over night it takes many years, so it will take some time and a lot of effort to improve its situation, it may never become perfect but it will become passable for its age. That black case of mine is a hundred and fifty plus years old with its original leather so as I said take your time and feed the leather often.
The final finishing polish I have always used is "Shoe Restoration Polish" it has lots of added colour dye added leaving a good deep shine.
Finally if you have to glue leather purchase the correct leather adhesive for hard ware places though for normal sticking back the odd scuff flake and cuts PVA works well