Wholesale used-vehicle price erosion continued to an extent in May, according to two major indicators. One of those, the Manheim Used Vehicle Value Index, recorded a second-straight month of decline. Cox Automotive said Wednesday that its Manheim index — a measurement of wholesale used-vehicle prices calculated by tracking vehicles sold at Manheim's U.S. auctions and applying statistical analysis to those figures — fell 2.7 percent in May from April. Cox adjusts that figure for mix, mileage and seasonality.