The rear gear cassette made ever louder noises since i left Qaghiliq, so 5k out of Yarkand - where I hoped to stay overnight - I took a look. The cassette was loose again, so I spent over an hour to assemble it correctly (remember the individual rings were no longer attached). A bit risky if it hadn't worked out as changing the cassette would imply changing many other parts as well, but i was concerned with the derailleur being damaged...