A long-standing feud over Chinese restaurant’s supply of duck sauce has been linked to the recent slaying of a deliveryman riding his scooter through Queens. Yan Zhiwen, 45, was gunned down on Saturday night in Forest Hills, with witnesses describing a Lexus SUV that then peeled away from the scene of the crime. The vehicle is the same type driven by a notoriously irate customer of Great Wall, the eatery where Yan worked for over a decade. The unnamed customer, now actively being sought by New York authorities, first clashed with the restaurant last November, complaining to the owner that he’d not received “enough duck sauce” with his order. Denied a refund, the customer allegedly returned in January to threaten the owner with a gun, slash his tires, and damage the restaurant’s locks, police sources told New York Daily News. The customer, according to authorities, has an arrest record stretching back to 1995 that includes at least one incident of armed robbery. A customer at Great Wall described Yan to the Daily News as a “wonderful, wonderful person” who cared about everyone. “I can’t believe he’s gone now,” the customer said. “This is just such a shock.”