My cladding is really really dark and it has happened to me too i cant get it to come off, it made my cladding look completly gray on that spot, this happened like 6 months ago and its still there i use armor all to cover it up, but as soon as i wash it off it comes back, that stain wont come off. i dont know if it is because my cladding is really dark but nothing i have tried has actually made the stain come off