Some updatings:
After the grinding of the head (the valves were OK !!!

) my MB dialer has looked for coming to a compromise:
I don't pay anything else that the new 4 injectors (1440€).
Is it right for you?
Is it possible that there wasn't any explanation for what happened?
Pls I'm waiting your suggestions.
Some additional informations: my A-Class 170 CDI W169 covers a distance of 104000 Km and I bought it in 2001.