EA8160 leaking

Hello everyone
,I soon despair of the EA8160. It started from one cup to the next that water collected under the machine and in the drip tray. I disassembled the machine and found that the water is mainly coming from the center hose of the drain valve. It's already leaking out of there during the brewing process.

Since the valve is not available separately on this model, I bought the whole water manifold including the drain valve new and have the same effect.

After brewing and opening the plunger, water is still in the brewing unit and rises 2-3 more times before draining down into the drip tray. The seals of the plunger still look good, also under the brewing unit the rod is dry.

So coffee is coming into the cup, but water is already leaking out during brewing and again afterwards until the brewing unit is empty. The marc is wet.
Does anyone have any idea what could be the cause?
Many thanks in advance.
Greetings Olli