Hi,
You have to know there are different qualities of leather.
When leather leaves the tannery it´s a 1 cm layer, very thick.
Then the process is to split this thick layer into 2-3 thinner layers.
The best of it is the first layer which has the "full grain", jackets gloves and fine cases are made with such leather it will last ages and mostened once in a while they will resist.
The second and so on layers will never have the firsts one quality or resistance.
For making these secondary layers fit for work tanneries emboss patterns and paint them with plastic coatings.
The cases such as the rolleiflex´s and the well known leicas are made of secondary leather layers, they are painted and with ageing they lose there humidity and crack like card board.
NEver use oil, if it is in one piece with no cracks you can repaint it, even you can fill the cracks with some edge dressing from fiebings and then paint it.
🙂 Good luck!