DIAGNOSIS Yeah, grease and steam can get past the inner door seal and condense on the inside of the outer glass panel. It's a design flaw—the glass isn't meant to be separated for cleaning.
FIX The official, safe method is to use a long, narrow tool wrapped in a microfiber cloth. Dampen the cloth with a mix of warm water and mild dish soap. Carefully insert it into the gap between the inner metal door and the outer glass frame to wipe the inside of the glass. Be gentle to avoid scratching or dislodging the glass.
IF THAT DIDN'T WORK To prevent future buildup, always let the unit cool down with the door slightly ajar after cooking. This reduces the vacuum effect that sucks grease-laden steam into the gap. Wipe the inner door seal (the silicone gasket around the metal door) after every few uses.
HEADS UP Do not submerge the door assembly in water or try to pry the glass out. The door contains wiring for the door-open safety switch. Getting it wet can cause a short, making the unit think the door is always open (and refusing to start).