The beauty is back! 
Thanks for cleaning-advices.
Wow! that looks brand new now. Are you done putting it together? It may be the angle, but nozzle seems a bit too close to the heater block.
@Alex_Lee Nozzle was fully turned in, then turned back 1/4 and then I turned the heatbreak against the nozzle.
What did you end up doing to clean it?
I let it soak in Aceton for a few minutes, the debris on the cooling-block was instantly gone. The hard black stuff on the heater block was then scrubbed off with a brass-brush I had at hand. The nozzle is new, the thermistor is set in with termal-compound and the heater itself was in good shape.