If the leather is ok and not ripped and it is just the colour which has faded then a couple of coats of good old fashioned shoe polish will do the trick. I have had cars before with black leather seats where the colour has faded quite bad. After it had a good soak with Kiwi parade gloss black leather shoe polish they came up as good as new.

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E90 318i 2007 N46 2.0 Manual
E53 X5 2004 M54 3.0 Sport Auto
E83 X3 2004 M54 2.5 Auto