Just a wild guess but what about plain old saddle soap? I have a Stressless leather recliner and the upholstery guy told me just a damp cloth for most smudges. If neither ideas appeal, Richard would sure be the next stop.
Ok this may sound odd but bathroom cleaner like Kaboom or Srubbing bubbles will do the Trick and clean almost anything off with a soft brush. After you work it in and it lifts off the dirt and grim dry it with a town and it will capture all the dirt.
The only thing you must do when everything is cleaned and stripped of all the dirt is seal it with good leather conditioner like people have said above.
I have used this method many times with great results.
Thanks all. Ordered Zaino. Forgot they had leather cleaner. I know I was able to get a nasty scuff out of one of the seats with the Mr. Clean Magic Eraser the day I got the car, but I was worried repeated use would damage the leather.
