Do you happen to know, or anyone for that matter, what these bearings are? Are they simply 608zz type and the 8mm smooth rods go into them? If they are 608s I would open it up and replace them with better bearings as I have purchased a lot of them from China and some are so-so to down right garbage but my step son was using 608s ABEC 5 on his skateboards growing up as a teenager (he would spend all day skateboarding many days of the week back then at skateboard parks, etc...) and those things would last in a printer for a decade I think, lol.