Got tired of trying to repair leaking toilet - leakage was due to the original parts not falling back to place. 
Investigated the mechanism of my toilet to figure out how it works & removed all parts that were not functioning; drilled a hole in the part that lifts the “plunger”, put a bolt M8 through, put the bottom part on it, then screw 10cm thread rod in. 10cm for my toilet is just enough so the thread rod to reach the hole in the lid.
Screw the top on the thread rod and its finished - to flush you simple lift it up to release water, when you let go, it all returns back to its place.
The weight of the thread rod helps with the return .