Lexus (in the owner's handbook) recommends cleaning the leather with a weak solution of wool detergent in warm water, do not soak, then dry with a clean cloth.
Lexus does a leather cleaning kit which works really well at removing dye transfer and includes a sealant to help prevent further staining. The only downside is it smells quite 'chemically'. Understandable as the Japanese don't like the smell of leather.
I wouldn't use a conditioner on modern automotive leathers as generally it is PU sealed and the conditioner just sits on the surface attracting grit and dirt, which if left in creases can cause cracking.
I had the interior of my Mercedes retrimmed in a naked nappa leather, the most sumptuous feeling but my word was it very high maintenance!