Coffee tastes "metallic"

Hello dear coffee lovers

We have had our Moltio HD8766-1 for about 8 years.
We have changed the brew group once over the years.

The machine is always regularly descaled, cleaned with grease remover tablets and kept clean in other ways.

We have a very nice crema

However, the coffee has tasted kind of "metallic" for some time now. The following measures have not changed this:

- use a different type of coffee
- change the grind
- change the water temperature
- insert a new water filter
- change the bean type setting (Arabica etc)
- clean the grinder with special beans
- leave the descaling agent to work overnight.
- clean the outlet nozzle with a fine, fine-grained tablet. Cleaned the outlet nozzle with a fine long brush for coffee machines.
- Changed the seals on the brew group
- Rubbed all seals with a little silicone grease
- Dismantled and cleaned the brew group filter.
- Minimally tightened the spring with the plastic ball of the brew group.

Now I'm at my wit's end.

Can anyone help?

Greetings
Oliver

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Meine Maschine: Saeco Moltio HD8766/01