Although the GSEs ended 2012 with $20.11 billion of pending and disputed buybacks on their books, the halcyon days of loan repurchase disputes may be behind the two, causing both Fannie Mae and Freddie Mac to reconsider their employment of outside due diligence vendors. According to executives who work for these vendors and serve as consultants to the GSEs, over the past several months Fannie Mae has slashed contracts with at least two outside firms…