Oil Filler Cap - how to take it apart
Lay the cap upside down on a good support
Press down on the filler stem and twist until the cut outs are matching the latches , let go
The spring will move the stem up and the mechanism comes apart
Now you can change easily the gasket, replace the spring if needed and verify the quality of the tabs and the rivets of the filler stem.
Revert the process for assembly