Concealed Cistern Flush Won’t Stop Dripping

[deptfed]

The flush mechanism in the concealed cistern of my toilet will not stop dripping - I have removed the mechanism, cleaned it thoroughly to remove any limescale, and replaced it with all notches lining up correctly and the ring screwed very tight. This slightly reduced the dripping but it is still dripping once every few seconds. Video and image of parts is attached - would really appreciate any advice on parts to replace or other things to try.