Thanks once more to all of you! I really appreciate your help!
So, today I pulled the clutch cover and confirmed what we all think. There is white greasy stuff. The oil screen looks good. The oil does look more or less normal (I would say).
The guys in the "KTM"(?)-shop know less than me (in that case) and look at me as if I was an alien when I show and explain what i think. I even showed them your posts, in spanish. They do not reaaly seem to be interested. Not sure if I hurt their pride by showing them that most of what we did yesterday was not neccessary (I told them from the start that we should check the coolant issue and they said it was fine)
I said: order all the parts we most probably need. But no, he first wants to be sure what exactly we need and says in the same time that it might take 3 weeks (from Austria). Do you think he would make an effort to find out WHAT EXACTLY we need?! It is ME who is wrenching...not sure if I want to lay my trust in their hands but now I have 10000 parts everywhere and hope that the guy knows where they all belong...