Thanks to the help centre, I was brave enough to pry off the mesh filter and take the unit apart. Turns out, the broken o-ring that popped out on my first use must have been an extra; there is no missing o-ring! So, I finally got to make my second espresso today. Back in the game!
I'm in the same boat. One o-ring was broken from the get-go and I don't want to damage the screen to replace it. Help!