1. sand it til you can hardly see the cracks - as much as possible. don't worry about losing shines.
2. apply generous amount of leather food e.g) Pecard. leave it for a day or two. do it again. repeat like for a week.
3. buff it til it gets shine using cotton towel

this is how i got my 50 year old Adga re-shined. it was in quite hopeless shape.

before


sanded


dressing + dressing


after


on