Im pretty happy with diluted APC or zaino leather in a bottle, but others have thier opinions as well. Since the vehicles I have used those products on were not tore up (you have a g37 so i doubt its tore up) both performed very well. Ive also had some decent results with Megs Leather cleaner, but it can be kind of greasy if over applied, but its a good OTC product.
I use Adams Leather Cleaner and Leathermasters products, both are very effective in removing trapped dirt
leather masters is great. if you want an all in one einszett Leathercare or Sonax Leather Foam are great!