I have 1 2013 X3 with oyster leather seats. only 2 mos old. I already have brown leather belt stains on the lower back of the seat that I CANNOT get out. I have tried just about everything that won't cause damage to the leather. I have read about the 4 to 1 or 5 to 1 Woolite cleaning recommendation, but have not tried that yet. Apparently the leather stain from the belt "transfers" to the lether seat. It doesn't just get on the top surface of the seat - it actually goes into the leather!!! (I think this is what happens with the blue jean dye too) I LOVE look of the white leather against the black lower color (my car is the vermillion red), but be aware about the staining. I paid for the Cilajet paint treatment when I bought the car and was under the "impression" that they treated the seats with something too, but after looking at the belt stain, I don't believe it!
If anyone has recommendations for getting the stain out - I am open to suggestions. I DID order some Lexol leather cleaner, but it has not arrived yet.