This isn't technically a Broadway flop, because it never made it that far: "Phantom," the story of you-know-who, by Maury Yeston and Arthur Kopit. The producers, who included Geoffrey Holder, were raising money for a Broadway run, secure in the knowledge that they had an exclusive license from the Leroux estate to adapt the book. However, when a certain well-known British composer announced plans to open in London (where the copyright had apparently already expired) and then on Broadway when the book entered the public domain, funding for the other production dried up.
The show, which has the structure of a Broadway production (e.g., a key song before the intermission), has lovely music, a less cynical take on the Phantom, and a sweet love story between him and Christine. Carlotta is deliciously villainous. Y&K's "Phantom" plays just about yearly in regional theaters, and is worth seeing.
Audrey, the Phantom Phanatic, who nonetheless would rather be Jean Valjean, who knew how to make lemonade out of lemons.