“Scotty and the Secret History of Hollywood” wears a lot of hats, none of which quite fits. A salacious tell-all about the hidden sex lives of postwar movie stars; a peek at the underbelly of the repressive moral dictates of the studio system; a breezy biography of a self-described Hollywood prostitute and procurer; and a psychosexual study of a possibly damaged victim of extreme childhood abuse. Only the last offers a clue to interpreting the movie’s more astonishing revelations and unprobed corners. Until then, Matt Tyrnauer’s gossipy portrait of Scotty Bowers, an impish nonagenarian and former Marine, listens without judgment as he describes decades of servicing the closeted hungers of stars like Rock Hudson and Katharine Hepburn, helped by an eager network of World War II buddies. Back then, in a couple of trailers behind a gas station on Hollywood Boulevard, $20 could buy just about anything. Meandering behind Mr. Bowers as he shares faded photographs of extravagantly endowed young men and prurient factoids about his famous “tricks” — cheekily illustrated with scenes from classic movies that read rather differently in hindsight — Mr. Tyrnauer surreptitiously hoses away the layers of dirt to reveal the fragility of his subject’s anything-goes hedonism. Benevolent hustler (he never took a cut of others’ action) or naughty fabulist — perhaps both — Mr. Bowers putters around his hoarded Hollywood Hills home and gazes into the hole in his patio deck as if searching for something lost long ago. Consequently, what starts out salty ends up as something sadder and more complicated. And when he unabashedly recalls a childhood rife with sexual encounters — which he insists were consensual — with adults, the camera fixes on his mile-wide grin and we wonder if his mission to meet the needs of others has somehow ignored his own.