How do you fill gearbox oil on a xsara Picasso?

To fill the gearbox oil on a Citroën Xsara Picasso, first locate the gearbox fill plug, typically found on the side of the gearbox. Use a socket wrench to remove the plug, then use a funnel or a squeeze bottle to add the recommended gearbox oil until it reaches the fill level, which is usually just below the fill hole. Reinstall the fill plug securely to prevent leaks. Always consult the vehicle's manual for the specific type of oil and the correct procedure.