O'Reilly Automotive (ORLY), which sells automotive aftermarket parts and equipment, is retreating after research firm Piper Jaffray downgraded the stock to Neutral from Overweight in a note to investors earlier today. A number of other companies in the same sector are also declining in the wake of Piper's downgrade. O'Reilly and its peers will face increased headwinds into 2014 and 2015, when fewer vehicles will be 6-12 years old, Piper wrote. Vehicles in that age range are the most likely to be repaired, the firm explained. The firm is also worried that waning auto parts inflation could hurt the sector, whose sales and margins have benefited from such inflation, according to the firm. Piper lowered its price target on the stock to $85 from $102. In early afternoon trading, O'Reilly declined $2.08%, or 2.27%, to $89.57, while The Pep Boys (PBY) dropped 2.52% to $10.04 and AutoZone lost 1.57% to $35.20.