Takeda just answered me.
They tell it's "normal" as they use stainless 409 (or an other way to say cheap stainless?). They suggest me to clean this mess myself.
As for the loss, if it is diagnostized, they will replace the parts that will need to be replace, that's all.
I'll try to contact them myself again to argue with them, but I think I will get stuck with a rusty exhaust.
