There seem to be some stains on the shutter.

IMPORTANT: This article applies only to specific products and/or operating systems. Check the Applicable Products and Categories section of this article before starting these steps.

The streaky lines and/or smears that appear when the shutter curtain or shading curtain is closed are patterns made by the carbon material used in the shutter blades.
Due to individual differences, the markings may be more noticeable on some cameras than depicted in this image, depending on the direction of viewing. Since these markings are patterns on the material, however, they do not affect performance.

• When viewed from the front
  
• When viewed from above at an angle