Phineas And Ferb: Season 2, Episode 40

2 - 40: I Was a Middle Aged Robot

Lawrence's memory is accidentally erased by a gadget in Perry's lair before participating in a father-daughter race with Candace, so Perry operates a robot version of Lawrence to fill in for him. Meanwhile, Dr. Doofenshmirtz invents an opposite of glue named "Eulg," which breaks stuff apart rather than join it together.