The Oracle of Omaha hasn't purchased shares of his favorite stock in more than a year, which brings stock valuations squarely into focus.In roughly 10 weeks, one of Wall Street's greatest investors will ride off into the proverbial sunset.For the last 60 years, billionaire Warren Buffett has dazzled investors with his ability to spot amazing deals hiding in plain sight. Since taking over as CEO of Berkshire Hathaway (NYSE: BRK.A)(NYSE: BRK.B) in the mid-1960s, the aptly dubbed Oracle of Omaha has overseen a ...