If you replaced the Douglas valve and the ball cock assembly and the flapper and your still losing water try the following.
Take the refill tube out of the over flow pipe and look down this tube with a flash light.
Sometimes the brass over flow tube seeps around the threads and you can see this looking down.
If this is the case take it out use joint compound and re install
Also if your using a 400A type of ball cock make sure you follow instructions in the height of the refill tube as it should be higher then the supply to prevent syphonage.
Good luck