This water faucet is on the wall outside of my house. As shown in the following video, when gradually turned on, it leaks from the above. It is as if the green hexagonal cap is not sealed due to missing part. If turned on enough, the water stream can become quite forceful that it can hardly be described as only "leaky". I forgot when i first discovered it if any part under the cap accidentally came off and got lost. I don't recall noticing any. I don't know what the part from where the water stream is leaking out is called. What part do I need to buy to fix it? Do I need to replace the entire metal faucet?
video that where and how the leaking happens: https://photos.app.goo.gl/1DdiSeGceGRhfjVu6