When Grampa was young he worked as a shoe-shine boy at Springfield Union Station. One day Clark Gable was his customer, having got off the Tinseltown Starliner to, as all the celebrities did, stretch their legs on the way to Hollywood, and went to Abe for a shoeshine. At this time, Gable had yet to hit the big time and was still an extra, just about to hit the big time, and Abe recognized him in his final extra role in Du Barry, Woman of Passion.
Abe asked Gable why he wasn't a star yet, to which Gable jokingly remarked that he ears may be too big. Noticing Abe had a book nearby, Gable asked him what he was reading. Abe revealed it was Gone with the Wind, and gave Gable his copy of the book, pointing out it only had one ("not a very good") swear word in.
Having finished his shoe-shine, Gable gets up and starts reading, saying "garbage, garbage, my line" twice and then noting "the burns, nice dresses" before saying he liked it and jumping back onto the Tinseltown Starliner, thanking Abe and telling him not to tell the story for sixty years as the train pulls out.
An "edited for seniors" version of the film was shown at the Springfield Retirement Castle. Scarlett O'Hara asked Rhett Butler (played by Clark Gable) where she would go and what she would do. Rick told her he loved her, and said they should remarry, with the film abruptly ending there. The majority of the seniors loved this new version, not noticing the differences, with Abe being one of them to show his approval. However both Bart and Hans Moleman criticized the cuts, of the swear word and the war, respectively.
Many years later, Abe told the story to Marshall Goldman, who put it in the Springfield Shopper. Lisa read the article, which had Abe noting that Gable owed him a book and never paid for the shoe-shine, but his "big blue eyes" could melt your "lunch butter".
Later when Homer saved Abe's life, Abe saw Gable as a ghost. Ghost Gable finally paid for the shoe-shine with a ghost quarter, saying he'll be able to use it pretty soon.
By all accounts the dates in this story do not match up. Gable's final extra role in Du Barry, Woman of Passion was in 1930, and this would match up to Abe's approximate age in this story. Gone with the Wind was published in 1936 and the film rights also picked up this year, pushing this story instead between this date and the 1939 release of the film, or even more specifically the 1938 hiring of Gable in the role of Butler, which however would not fit Abe's young age as he would soon be fighting in World War II, and would completely ignore the fact was a big star by this time, having starred in 29 movies by 1936 with a further six between then and 1938.
However, in reality the story seems to be as much a work of fiction on Abe's part as anything, as many of his "rambles" of the past are (for instance he later recalls being on the set of a Warner Brothers cartoon).