Unfortunately, my search for answers has been unsuccessful so far. Here in the forum nobody could help me so far. In the net you can find a lot of instructions for the dismantling of different devices, but not for the Krups EA 850b or similar devices.
Nevertheless now a short intermediate result:
The upper part I was able to disassemble and got to many parts of the machine. Side part and back part (connected) had to stay at it, because I couldn't get through there. By spare part lists one can understand that it would have to continue probably with the front part. How exactly is not understandable for me however.
With some skill I could clean the machine however thoroughly. The brewing flask (if you call it that) can be removed and cleaned with some skill. The newer system has two gaskets, but both had aged a bit in my case. In the meantime I have ordered some more and will reassemble the machine with the new gaskets. Then, at least I hope, the biggest problem should be solved.
Should someone still know how to dismantle the Krups EA 850b, I would be very happy about a hint.