Rusky,
The answer will largely depend on the type of leather and the amount of damage. If the leather is a full hide (not split), and it is not treated with a vinyl film, the treatment is to clean and protect with Hide Food. You can soften the dry spots by treating once a week or so until the Hide food gets worked in and hydrates the leather again.
If the seats are a split hide and treated with a vinyl coating, you have a bigger problem. The vinyl coating is designed to keep moisture and stains out, making it difficult to re-hydrate the hide. Under a microscope, you'd actually see that the vinyl coating is not a perfect seal... it does have very small holes, because the hide must be able to breath. To re-hydrate, use a thin, water-based protectant or a solution of Neets foot (sp?). I suggest starting with 303 Aerospace as a first step.
If your leather has started to crack or if the dye is coming off/faded, you have a bigger issue that tretment will cure. There are leather restoration systems available.
db