This part is straightforward.
The only o-rings that need maintenance are the three ones located under the end cap.
There are more o-rings in the camera (e.g., around the lens or inside the end cap) - you should not touch these.
The most important thing to pay attention to is that the o-rings are always shiny, clean (with no debris, hair, or dust on!), and have no scratches or breaks.
If the o-rings look dry, you should put a thin layer of o-ring grease on. You can use your finger, tissue, or brush to do so.
Please note that putting too much grease on the o-rings might cause the camera to flood.