I have the same condition with my D700. I hesitate to call it a problem, since it in no way effects the presentation, or functionality of the camera.
I'll bet most of the D700's have similar...but most people just don't look that closely. I discovered my streaks quite by accident. Once I figured out that they didn't make a difference...I forgot about it.
Just FYI so that you don't think you're out there by yourself with a one of a kind issue.