The motorcycle frame and the rear swing arm were completely disassembled, the bearings from the swing arm will be replaced later. The frame was first cleaned with a parts cleaner and washed afterwards.
Here I also noticed: Both fork legs are unfortunately leaking and must be provided with new sealing rings at least (later it turned out that these are damaged too far).
This needs to be put back together afterwards… 
cleaning the chassis frame 
the cleaned chassis frame 
Some oil and dirt from the chain on the swing arm 
cleaning the swing arm
I can now transport the cleaned parts into my apartment and assemble them further in the living room.
cleaned chassis 
cleaned rear swing arm 
chassis and a curious cat 
chassis and rear swing arm
Actually, the replacement of the steering head bearing can turn dramaticly, but here they have actually made grooves inside the frame, where you can easily remove the bearing shells with the appropriate tools. But the steering head bearing is in best condition (greased, clean, free of play) and stays in there for the time being.
However, it turns out that the bearings of the swing arm are all worn out: The needle bearings were mostly filled with water and are completely corroded.