The vibration pump is changed. I used PTFE tape and the operation was fairly simple. Pump is working!
I filled the boiler - emptied it - filled it with descaler - waited 45 minutes - emptied the boiler - ran through 1,5-2 liters of fresh water through the group and steam arm.
All is well. Pulled the first 4 espressi - just great stuff.
(i have not checked what happened with the old pump - but as was mentioned I would have a look at it and have it as a spare for future)