We must have different containers of citric acid. The one I have is the MB blue color with the MB star and some German and maybe French writing and of course English. The only English is inside a box in the middle of the label and it states:"In case of eye contact flush thoroughly with water. Do not take internally. KEEP OUT OF REACH OF CHILDREN!"
About removing the thermostat after the citric acid flush and rinsing thoroughly with clear water; The instructions in the Factory Manual clearly states to remove the thermostat before starting the cleaning process. Therefore the thermostat should not be installed during the flushing procedure. If you had ever flushed a Mercedes cooling system using the method in the Factory manual, you should have remembered this. Another thing you might recall is that the concetrated lemon juice used in the acid flush will not harm your hands.
Bill Lewallen Lexington,Ky. Home of LexMark Printers