I am using a 20x80 v-slot rail with solid delrin v wheels for the Y axis on a prusa style 3d printer. I have started noticing some black particles on the rail and some wear on the wheels they have been in daily use for a couple of months. It's not enough that I can feel any play yet. Just trying to figure out if this is normal or if I have an assembly error. Should I be using some kind of lubrication between the wheels and the v-slot?