LOS ANGELES • Four decades have passed since the Rydell High gang twisted, hand-jived and crooned their way into the hearts of teenagers the world over, but many are still hopelessly devoted to Grease.
The classic musical, which is celebrating its 40th anniversary, took moviegoers back to their high-school days with girl-next-door Sandy (Olivia Newton-John) and bad-boy T-Bird leader Danny (John Travolta).
"When we finished it, we really didn't know what kind of impact it would have," said film-maker Randal Kleiser, who made his feature-length theatrical directing debut with Grease.
"We thought it would do well with teenagers for a summer or two, but never thought that, 40 years later, that amazing amount of response from all over the world and all ages would happen."
Based on a hit Broadway musical about the love affairs of 1950s high-school students, it was shot over two months in Los Angeles for US$6 million and was initially eviscerated by many critics.
But it ended up grossing almost US$400 million and was the most successful live-action movie musical of all time until Mamma Mia! 30 years later.
When Kleiser cast his leading couple, Travolta had already filmed Saturday Night Fever (1977), but it was not yet released and he was largely known as the young heart-throb from ABC sitcom Welcome Back, Kotter (1975 to 1979).
Newton-John was a pop music superstar, with several hit records under her belt.
"John and I both wanted Olivia and she was resistant because she'd done a movie that didn't do well in England, a sci-fi movie, and she thought she might be a little too old to play opposite him," Kleiser says, referring to Toomorrow (1970).
"She requested a screen test and we did it. John and I both treated her like a little sister, gave her all the encouragement and it worked."
Travolta and Newton-John have remained close friends over the decades, starring together again in 1983's Two Of A Kind, a flop by any measure, and reuniting in 2012 to make a Christmas album.
They swop text messages and have supported each other through dark times, including the death of Travolta's son in 2009 and the return of Newton-John's breast cancer after she had beaten it in the 1990s.
Kleiser said that while he had seen his stars separately over the years, an anniversary get-together at the motion picture academy in Los Angeles next month would be the trio's first full reunion.
The director made other movies after Grease - most notably The Flight Of The Navigator (1986) - but the lure of big studio blockbusters lost its lustre and he moved away from the Hollywood system in the 1990s.
He believes the film's longevity can be attributed to its universal themes, the chemistry between his leads and its appeal to people's nostalgia for a more innocent age "when there were no terrorist attacks or shootings".
"That all came together in a perfect storm and hit the public zeitgeist," he said.
Travolta became a global superstar and his career highlights in the intervening years - another 30-plus movies - barely need rehearsing.
After a lull in the 1980s, he underwent a resurgence sparked by an appearance in Quentin Tarantino's 1994 masterpiece Pulp Fiction that made him an icon for a whole new generation.
Newton-John kept her music career going and went on to appear in Xanadu (1980) and Two Of A Kind.
She says she still has the skin-tight black pants she wore in Grease.
Kleiser still goes to screenings, but says he prefers these days to watch the audience experiencing and enjoying his crowning achievement.
"I see lots and lots of flaws in it, but I think the flaws are part of the charm of Grease - the fact that it has a rough-around-the-edges feel," he said. "It's not real slick - everything is not perfect - and I think that adds to the feel of it."