I've attached a photo of the part that is missing in your photo. It looks like a regulator, but I'm not sure what it does. I had to lay down on my back under the SEE in ~5 deg. F. weather to take the photo, so I didn't stay there very long! Someone else may recognize the item and know what it is. As Guyfang suggested, you should definitely download the TMS and the Student Handout if you haven't already. I would also recommend identifying yourself and your SEE and reading all of the posts in FLU419 SEE HMMH HME Owners group . It is very long, but there is a wealth of information there.