Hmm...I suspect it is leather conditioner. Many dealers wipe the seats down with leather conditioner and many of the conditioners are white liquid. These seats do not absorb conditioner very well and if it sat on the leather for a while, unabsorbed, it may be starting to become more visible to the eye. Try wiping the seats down with a good leather cleaner and I bet the white residue goes away. My favorite is Pinnacle Vinyl/Leather cleaner.

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~ 13 M3 coupe "new" daily beater
~ 13 x5M Hers
- Previous BMW's - Way too many to list here (15)