In a stark reminder of how some battered financial firms remain dependent on government lifelines, GMAC Financial Services Inc. and the Treasury Department are in advanced talks to prop up the lender with its third helping of taxpayer money, people familiar with the matter said.The U.S. government is likely to inject $2.8 billion to $5.6 billion of capital into the Detroit company, on top of the $12.5 billion that GMAC has received since December 2008, these people said. The latest infusion would come in the form of preferred stock. The government's 35.4% stake in the company could increase if existing shares eventually are converted into common equity.The willingness by Treasury officials to deepen taxpayer exposure to GMAC reflects the troubled company's importance to the revival of the auto industry. Founded in 1919, GMAC has $181 billion in assets and is a major financier for 15 million borrowers and thousands of General Motors and Chrysler car dealerships in the U.S.