I bought a new lens, and discovered two stains/spots which look like water spots on the rear side (side which is plugged to the body). These stains are from the inside. I have taken a couple of pictures but so far not discovered any problem. In some articles I read that a certain amount of dust comes ever with new lenses. Is it normal to have such spots even in a brand new lens (original Fuji)? Or shall I rather request an exchange of the lens?