Here the feedback of the source of my shaky (no more working) brake problem.
The primary source was the aluminum bolt between the holding screw and the caliper. As you can see, the bolt is worn on the caliper arm, that holds all the weigth of the brake system. Also the holes of this caliper arm are expanded / outworn (short before cracking). The outer arm of the caliper is fine. Also no damage on the bolt.
A friend of mine had the same problem. His AMEL 54 is nearly the same age as mine (2009).
Amel was very helpful and they send me the new caliper now. The new model already discussed here in the forum.
I hope it fit's into my caliper holding.
So it looks like it's something that will come up earlier or later on all 54's, since the aluminium bolt is not designed (or underdimensioned) to hold the weight of the braksystem a livetime....
I have 1.700 engine hours.
AMEL 54, #144