My Flair 58 plunger is not traveling smoothly through the brew head.

With use, the plunger will naturally lubricate thanks to the exposure to coffee oils. However, you can expedite this process by applying a light application of food-safe oil (i.e vegetable oil) to the plunger o-ring and wiping away the excess. It is also good practice to do so after cleaning the plunger, as you will be removing those oils once again. 

Additionally, ensure you are completely filling the chamber with water prior to the start of your extraction. If not, there will be air bubbles, and the resistance you feel may be due to those spontaneously compressing, or the plunger tilting beyond tolerance as a result. Always use your Stem Guider to ensure the smoothest, most consistent traveling of the plunger if you do not have the 3-piece lever hook.