Fellas, I'm new to the off road bike scene, but I'm no newbie. I've never seen this on any of my other motorcycles, so I'm hoping you guys have seen it on your bike at some point. I have black streaks that appear lengthwise on my inner fork tubes. What causes this? How do I remedy the problem? Is there a way to remove them? I bought my bike used, and the more I look at it, the more I realize it's been beat down. 2007 DRZ400SM. Thanks guys!