Pullrite Superglide 18K ISR Unhitching

Yeah. I know I'm going to have to practice and practice to get the hang of it. At least now I know I'm suppose to back up some to release the weight/tension on the hitch. I fully understand the rationale behind that. I've only had the hitch over a month and still in the back of my truck and I've taken the trailer out a couple of times now. I've lubed the way tubes as directed. With the hitch exposed to the elements and it being windy where I live, lots of dust/dirt has collected on the way tubes. I've cleaned off the dust and dirt and apply fresh WD40 to the tubes every time I take out the trailer; however, I noticed there appears to be some black colored streaks that I see on the way tubes mixed with the WD40. Could it be just old dirt mixed with the WD40? The hitch slides and I also applied WD40 to the inside of the hitch where the plastic wear plate is located. Just wondering. Want to make sure the integrity of the hitch isn't compromised.