We wanna talk Jon Larson? "La Vie Boheme" is full of it. For example, "Bisexuals, trisexuals..." on is a dead rip-off of at least the style of the long version of "Ain't Got No" in HAIR (the protest rally), and under "Hey, mister, she's my sister..." I'd swear to God that's the riff from "On Broadway," the song covered by everyone from George Benson to Eric Carmen.
Also, at least one song was completely stolen melody-wise from another writer's project, but Jon had died before he could be called out on it.
"There is no problem so big that it cannot be run away from."
~ Charles M. Schulz