Once the gate is open, fly again into emergency shaft [#1]. You'll get to the damaged room.
You'll find there [#2] massacred janitor. Grab him with tractor beam and take with you.
Fly along with janitor to the large cauldron [#3] and throw him inside. A green color should appear. Once you use the piston, a cabin closes and the game ends. After credits you'll fly out as a ... janitor. Congratulations, you've saved the robot!