I am trying to determine the cause of a wear issue on our machine. We have a 440c idler bar that rests in a slotted block made of delrin or UHMW conductive Polyethylene holder. The shaft rotates at ~1500 rpm. I am getting wear on the shaft that produces brown dust. The shaft is 8mm and the holder slot width is 8.3mm. The shaft is meant to be removeable to remove paper jams. Any ideas? Images attached.