Another episode requested in comments: a one-hour episode from the third season. Johnny takes on a new persona, "Rip Tide," when he's forced to sell out and host a TV disco show, and he finds himself enjoying the sellout life so much that his new persona starts to take over all the time. The plot flirts briefly with the idea that this is some kind of actual split-personality problem, but primarily it's about a familiar character selling out to become the embodiments of everything that was bad in circa-1980 culture and being talked out of it when he realizes that his friends -- and he himself -- can't stand his new persona. It's like a music-business version of Taxi's Vic Ferrari (who first appeared a few weeks after this episode).
Unlike the other two-parters I think this one probably would have worked better as a half-hour, since it really doesn't give the other characters much to do and therefore feels padded in spots. But Hesseman is great and there are some good sequences, especially the ending (which was ruined in the '90s syndication version when the Little Richard music was removed).
This is also an example of how shows have to move fast if they want to be topical. The episode aired early in 1981 but the story was almost certainly conceived in 1980 (it might have been done earlier if the season hadn't been delayed by an actors' strike). In 1980, disco and the anti-disco backlash were very big and the story was topical. By the time the episode went into production, disco had collapsed; Johnny gets a line about how disco is dead, but the story would have made more sense if it hadn't come out after disco ceased to be popular. In a way the story works better now because it feels like a late-'70s period piece whereas at the time it was already a period piece.
Oh, and the late Mary Frann, who had previously appeared as an attractive woman who turns out to be an evil bitch on The Mary Tyler Moore Show, here returns to the MTM lot to play an attractive woman who turns out to be an evil bitch. In case you're wondering why she always seemed miscast as the loving wife on Newhart.
This being an episode about music on TV and radio, it's filled with music, including but not limited to: "Land of 1000 Dances" by Wilson Pickett; Xanadu" by Olivia Newton-John; "Sympathy For the Devil" by the Rolling Stones; "Le Freak" by Chic; "I Love the Nightlife" by Alicia Bridges; "De Do Do Do, De Da Da Da" by The Police; "Blue Suede Shoes" by Carl Perkins; and "Ready Teddy" by Little Richard.