Thanks for the quick responds!
@Capo Sakke: I now it's not an oil, but used it anyway. You got to make a soltution with what you have. :-)
@Spooky: I'm sorry to say man, but it's not like you said. It's not f**ed up. It's still ok.
@Island Hopper: Thanks for the explanation how to get the slave cylinder off. And for the oil advice.
So i took everything apart and cleaned it properly. The only thing i could find Samarkand was the ATF oil. As there only a handfull of bikes in Uzbekistan. So filled the system with that, let the air out and everything works very smooth. Once home i'll replace it with the proper oil.