Krups EA 9000 hot water leaks out

My first post here and try my luck in this forum.

Problem: too much hot water leaks out via the drip tray on above fully automatic machines.

Previous knowledge: Electronics technician with previous knowledge from simpler coffee machines (classic KAMAs, pad machines and the like).

What happened so far: no leaks detected on visual inspection, drain valve on water manifold replaced. No improvement.

Now I'm a bit at a loss... what else could it be? I have the suspicion that my "customer" has not decalcified the device regularly, contrary to her assurances, and the pressure in the hoses is probably too high? Is this the right approach or nonsense? What happens next? I am glad about every hint!