Land Rover Series transfer box selector shaft cover, Land Rover part number 266956.
The genuine Land Rover item is currently not readily available so this is the Santana equivalent part which fits in exactly the same way.
The original LR design features individual covers for the two shafts. Mud gets stuck between the two caps and the cover eventually rusts out. In my opinion this Santana cover is a superior design, as both rods are covered by the same cover, therefore no gap to catch the mud.