A settlement between Ally Financial Inc. and Fannie Mae over soured mortgage loans could shed light on how banks will resolve repurchase demands with Fannie Mae and its sibling, Freddie Mac. Ally’s mortgage-lending unit, GMAC Mortgage Inc., on Monday agreed to pay $462 million to Fannie to cover potential repurchases on $292 billion in mortgages sold to Fannie. Over the past two years, Fannie and Freddie have stepped up demands that lenders buy back defaulted loans when they find that the mortgages didn’t adhere to their loan-purchase guidelines. Fannie and Freddie collected more than $9 billion from banks during the first three quarters of the year. At the end of September, another $13 billion in requests hadn’t been paid, including more than $4 billion that have been outstanding for more than four months.