“A look at the latest Broadway casts of ‘The Producers,’ ‘Frankie and Johnny in the Clair de Lune’ and ‘Oklahoma!’ has confirmed one basic truth of the theater: if the chemistry of casting is an elusive and mysterious science, the alchemy of recasting is even more complicated. No matter how much electricity performers give off naturally, when you plug them into roles that don’t fit, short-circuiting is to be expected.”