Depends on the liquid that caused the stain. The leather isn't cheap coated stuff, it's dyed through. I've used the leatherique treatment on seats that has removed some stains. What was the cause of the stain? What color?
08 E90M3 6MT Alpinweiss/Carbon/BPMSport 91 octane tune/BPMSport Feature coding/BMW Pedals/Dinan Exhaust/Alcantara Wheel/Rear Fog Switch/Rattle fixes