I think I have the same seats your referring to (although I know some are entirely white)
I have tried a few different products on them since buying my Z over 4 years ago.
I am currently using Astonish leather cleaner and Wheelers natural leather balm.
The Astonish was one of the cheapest leather cleaners I have tried, but I find it lifts denim stains & the like as well if not better than any of the more expensive products I have tried.
The Wheelers leather balm conditions and protects the leather after cleaning, and is supposed to help prevent stains.
The best (and most frightening) colour interior (except for the R) in my opinion.