AutoZone fell after a rival parts retailer, O’Reilly Automotive , said sales growth was slow this quarter and profit will be on the lower end of its forecast. The sector is slumping, said David Schick, at Stifel Nicolaus & Co. “It makes sense with more new cars sold . . . and the lack of a cold winter to cause parts breakage.” O’Reilly had its biggest decline ever, down 14 percent to $82.61.