The Maintenance dialog (found on the 3DPrint Tools menu) keeps a record of when the Fast Axis bearing, the Slow Axis bearing, and the Piston Screw require lubrication. 3DPrint will prompt you when lubrication of any of these components is required. Only lubricate these components when you are prompted to in 3D Print.
While lubrication of these items is important, it is equally important not to over-grease the bearings and piston screw when lubricating. Only a very small amount of grease is required to keep these parts working optimally. Over-lubricating creates a situation where lubricant builds up in places where it should not be, and may cause the printer to report an error.