The Lancelot tune-up part is available very late in the game on second playthrough onward, somewhere in last area (palace). On fourth and subsequent playthroughs, don't follow official story in order to get to palace. If memory serves me right, it's not inside any room, but hallways, hard to miss.
A: "Grr. Just what is the meaning of life!?" B: "Is there one in the first place?"