I ordered a 4 pack SCS8UU bearing I’m thinking of using on the X axis of my laser engraver from one of my favourite Chinese suppliers and had a chance to mess around with them over the weekend. On line I have read that they may be half the price of brand name but you should order extra. First off the oil (?) on them did not feel like oil and I think is more likely a rust inhibiter. After a good cleaning in Varsol I packed them with grease and 3 out of the 4 are now smooth as silk on an 8mm rod. The 4th one? The 4th one sounded like a tin can half full of gravel being kicked down a hill and I was honestly worried that it would damage the shaft. In for a penny in for a pound, I decided to take it apart. It came apart easily by just carefully prying off the seal and sliding the ball track out of the outer race. As I suspected there was dirt and a couple of large (relatively speaking) bits of metal in it. With everything cleaned up all that was left was to get all those little balls back into place. Luckily they stuck to the grease on the ball track and I hadn’t managed to lose any. Dropped the track back into the outer race, snapped the seal back into place and the bearing slides smoothly and quietly on the rod. Having bought tooling from overseas this was no surprise. I guess when you want it at a rock bottom price they have to cut corners somewhere. At just over a buck a piece you may have to take it apart and clean it yourself.