Ruede,
Glad to have you on TVWBB!
What you are describing is what a lot of our members call “The Dreaded Fade.” It happens the most with black hoods, but it can happen with others. It is an internal change in the porcelain coating. No cleaner, abrasive, etc. will take it off because it is not something to remove. I have a black Skyline hood on which I have just learned to put up with the faded top.
To make yourself feel better for a short time you can try the trick of “waxing” your hood with spray Pam. It sometimes does amazing things for a brief stint, but it will soon burn off or dry up.