Review on Iverntech MGN12 700Mm Linear Rail Guide With 2 MGN12H Stainless Steel Black Carriage Block For 3D Printer And CNC Parts by Mark Fleming

I ordered 3 of these rails to convert my Ender 5 plus. 2 of the rails slide as smooth as glass. The third one is rough and sticky, even after a good thorough cleaning. It has these dark areas in the rail groove that inhibit the block from gliding over it without some effort. Now it looks like I'm going to have to order another one. I had high hopes from the reviews.