All 3 options:
I. And brain grease works inside the loves like car grease works inside an engine
II. But weirdo me, I was born with too much grease inside my skull, and it got all thick and muddy and disgusting....
III. My thinking and breathing and living engine slowed down and flooded
All 3 options are written to engage the reader. They all compare the speaker's brain to a car engine. He uses the extended metaphor to make it easier for the readers to understand the effects of being "born with too much cerebral spinal fluid". The book is geared towards a young adult audience. The phrase "cerebral spinal fluid" seems too sophisticated and difficult for his target audience to understand so he breaks it down to a way that he feels his readers would better understand.