I been through all this. Rejuvinate, dye, etc. Let's make it simple. Once leather done it's done. Take cardboard, soak it in oil. Is it "pliable"? Yes. It's exactly what happens with dried out leather and "products".
@Ridies already responded with "clean with soapy water". Yes, this is it. And if you can - keep it out of sun. Tint your car and put windshield cover. Afterall our leather is 20 year old.. I was taking apart 20 yo BMW seats. Leather IS like cardboard, you can rip it with your hands. LX leather wasn't as bad. It's just old, not much you can really do. Buy new cover and move on.
Seats I painted (before on BMW) looked good for a while but it doesn't hold up. That's why I wanted to learn upholstery for myself.
P.S. Because upholstery so expensive companies that produce "snake oils" can advertise miracles. But in my experience... Maybe it's my own opinion. But. If leather shot it's shot. You can make it look good, paint, etc. But it won't last. Period.