Remove the End-Cap.
For cleaning, you will need:
Rinse the dirty O-Rng and End-Cap together in water, then remove the O-Ring and wipe down the End-Cap's O-Ring groove with alcohol.
There are two methods to grease your End-Cap.
Put a small bit of grease on your finger, then carefully rub it around the edge.
Remove the O-Ring and lightly grease it, before placing it back on to the End-Cap.