Record collectors and documentary filmmakers often look for the same thing: a moment when someone does something remarkable without being seen, a gap that turns the witness into a proprietary liaison between that moment and everyone else. Crate-diggers dream of finding that record, the one that sounds like music you know rendered in a version you don’t know. Maybe it’s a South African rock record with a clattering, popping drum intro or a forlorn acoustic song ready to drive home a Wes Anderson plot point. Documentary directors search for dogs in love with elephants and impossibly driven wire walkers, subjects that beggar belief but end up secured in the medium, confirmed and concrete. A new film by Malik Bendjelloul, “Searching For Sugar Man,” satisfies both the hunters and the general audience. How? To use technical language, the story is bonkers: Bendjelloul’s documentary is delicately balanced on an iceberg-sized peripeteia that is easily spoiled, so if you want to see this movie (currently in limited release, and opening nationwide throughout the summer) read no further. Or, go see it and come back.