Cleaning your Fenix flashlight is an excellent way to prolong its lifespan and protect it against damage from corrosion. Taking the time to proberly maintain your light is also an important step when troubleshooting issues with your light. Essentially, you should sway contacts and threading with alcohol, and apply a thin layer of O-ring lube to seals. All of this will guarentee healthy connections and proper assebly.
This video walks you through the cleaning process