I am new in the world of 3d printing, but very mechanical and electrical inclined. I have now been through a total of about 2 rolls of filament. After about the 1st roll, was having trouble with first layer. Ended up replacing the bed rollers, it was better again. Now after about a second roll, it is back to having problems again. When doing a manual bed leveling, it changes when moving the bed back and forth. The rollers are again showing wear. So to me it appears there is a problem with the bed assembly, or the track. I had been doing mostly small prints. Before I changed the rollers, I done a first layer test, several times. And there was always a distinct height change at distinct locations. The new rollers, temporarily made it better, enough to get a first layer down. New rollers every 3/4 of spool is not what I would call normal. When the machine arrived the rollers on the bed and the hot end were so loose it would have never printed anything, the machine was refurbished, it looked like maybe someone had tried to print something and returned it. Creality re-sold it, never checking it.It has been a great learning experience, just not sure if the problem is the rail (can not see or feel any defects) or the bed plate, can not tell if the rollers are running true. Or is it just bad rollers.