Nostalgia of a sort is flourishing elsewhere on the radio dial, however: After more than 50 years, the Marx Brothers were back on the radio Sunday. National Public Radio's "Weekend Edition" broadcast a variety of sketches culled from recently discovered scripts of the 1932 radio show "Flywheel, Shyster and Flywheel," in which Groucho played the wisecracking attorney Waldorf T. Flywheel and Chico starred as his inept assistant Emmanuel Ravelli. The 18-minute NPR broadcast featured Steve Mellor as Groucho and Mitchell Greenberg as Chico. Both recently starred in the restaging of "The Cocoanuts" at the Arena Stage in Washington.