You're right, Sonny: that's another inaccuracy that shifts the meaning. In the movie, Lefty is the schlemeil of the Mafia, but Brasco develops filial feelings for him, even offering him money to buy a boat to escape the Mob. In the book, Brasco acknowledges that Lefty is no, schlemeil, is a good earner and has clout (he prevailed over Mirra in The Big Sitdown), but he has no respect for Lefty and his constant whining and free-loading. Buthe has filian feelings for Sonny, and you get the feeling Brasco genuinely regretted that he in effect caused Sonny's demise.