In the old Astroboy mangas/show, Astroboy gets oil by having some device plugged into his butt. Strange, yet innocent, right? Well, think about it: This is a robot who looks like a nine-year-old boy. He's having a phallic-shaped oil-delivering object being shoved into his butt while EVERY OTHER ROBOT IN THE MANGAS/SHOW receives their oil by drinking it from a cup. Of course, it begs to be added that Astroboy is the ONLY robot that pretty much has no clothes on save for some underparts and shoes. The other robots have clothes. And remember: the creator was trying to make a robot replacement for his dead son... Pass the Brain Bleach, please.
In the 2003 anime, Dr. O'Shay speculates that the days Tenma spent with Tobio/Astro were probably the happiest days of his life. So what's the first step in Tenma's Villainous Breakdown? Erasing Astro's memory so he can relive those days.