Hello Thomas,
Okay, I had forgotten about that point. Occasionally, replace the pollen filter, and for cleaning, use warm water, then spray with Febreeze – that's all.
At the very least, when it starts to smell like dead cats coming from the ventilation slots, you usually replace the pollen filter yourself

.
My last but one cleaning was after approximately 2 years of operation, and it wasn't strictly necessary (there was hardly any leakage and no odor).
Where did the post go? Thomas had correctly pointed out the need for cleaning.
Best regards, Rainer.