Premise: Johnny Contardo (born December 23, 1951) is a former singer with the musical group, Sha Na Na which he left in 1983. In 1978, he appeared with Sha Na Na in the movie musical "Grease" as Johnny Casino and the Gamblers. His performance of the song "Those Magic Changes" was featured in the movie and on the soundtrack for "Grease".
Hypothesis: Johnny Contardo left Sha Na Na in 1990.