The silver-colored plastic steamer knob is pressed directly onto the steam valve shaft. There is no other part locking it on, as I discovered AFTER partially disassembling the machine. It's a very tight fit, so I used a large flat screwdriver blade to pry the knob off of my Magnifica, prying alternately on opposite sides of the shaft, a little at a time. I had to be careful not to mar the black plastic body behind the broken part.
Cafenpray, November 2010