Ray Bolger was originally cast as the Tin Man in the classic MGM musical The Wizard of Oz. However, he insisted that he would rather play the Scarecrow–his childhood idol, Fred Stone had originated that role on stage in 1902. Buddy Ebsen, who played Jed Clampett in the popular The Beverly Hillbillies TV series, had been cast as the Scarecrow, and now switched roles with Bolger. Unbeknownst to him, however, the make-up for the Tin Man contained aluminum dust, which ended up coating Ebsen’s lungs. He also had an allergic reaction to it. One day he was physically unable to breathe and had to be rushed to hospital. The part was immediately recast and MGM gave no public reason why Ebsen was being replaced.
When Jack Haley took over the part of the Tin Man, he wasn’t told why Ebsen had dropped out (and in the meantime, the Tin Man make-up was changed from aluminum dust to aluminum paste as one of its key components). However, his vocals remain whenever the song ‘We’re Off To See the Wizard’ is played. Jack Haley’s vocals were never used during the song, but were used for ‘If I Only Had a Heart’ and ‘If I Only Had the Nerve.’ Ebsen’s vocals are also heard in the extended version of ‘If I Were King of the Forest,‘ though the spoken segment has Jack Haley. Although no Ebsen footage from the film has ever been released, surviving still photos show him taking part in the Wicked Witch’s castle sequence.
The Scarecrow face makeup that Ray Bolger wore consisted, in part, of a rubber prosthetic with a woven pattern to suggest cloth. By the time the film was finished the prosthetic had left a pattern of lines on his face that took more than a year to vanish. –IMDB