I suppose at this point the damage is done. You could embrace the worn/patina look or repeat the process with the citric acid and remove the rest of the plating leaving the parts copper. Personally I think the copper looks nice and you could always replace or replate the parts any time since the machine is functional and the issue is only cosmetic.

RobAnybody wrote:Standard wrenches won't go through the fill opening, you would have to resort to removing the heating element and going via the bottom with a socket wrench (socket on a articulated joint with an extender pole). You"ll need a metric size 16 socket for that.
Cheers,
Rob

Very helpful. Then the tool offered by Stefano's Espresso Care is an option for going through the top. It would save time and may not cost more than a socket wrench with an articulated joint and an extender.