Gary Burghoff decidiu não usar o chapéu para o episódio final:
When it finally came time to film “Goodbye Radar” Gary decided he didn’t want to wear his hat. This became a big issue and remains a sore spot with me to this day. Our contention was that without the hat he no longer looked like a kid, he looked like a balding man rocketing into middle age.
Não foi dada nenhuma explicação na tela que eu saiba.
Talvez, como PaulStock apontou , você esteja confundindo o chapéu com o ursinho de pelúcia de Radar. De um artigo sobre mash4077tv.com :
“Good-Bye Radar (Part II)”
After Radar leaves the 4077th for good, Hawkeye and others return to the Swamp to discover that Radar has left his teddy bear on Hawkeye’s bunk.
... e, a partir da temporada final do show, bem depois que Radar saiu:
“As Time Goes By”
Hawkeye offers up Radar’s teddy bear, which was left to him: “Let it stand for all the soldiers who came over here as boys and went home as men.” Note that the teddy bear seen in this episode bears little resemblance to the one-eyed bear shown in every other episode.