Billionaire Carl Icahn's investment company offered to buy the 18 percent of auto parts maker Federal-Mogul Holdings Corp has been focusing on its auto business, its second largest by revenue, as a slump in crude prices slows growth in its energy business, which accounted for nearly half of its revenue in 2014. The company said in December it would buy auto parts retailer Pep Boys-Manny Moe & Jack PBY.N for about $1 billion.