Robert Morgenthau's stranglehold on the position of Manhattan District Attorney has lasted 33 years but today's Post tittered that he was mulling an "early exit." Page Six reported that a "well-connected legal source" said the 88-year-old DA was orchestrating a retirement to have Cyrus Vance Jr. installed for a few years. Apparently Morgenthau wants Vance Jr., once an assistant DA, in place to block his former protegee and 2005 Democratic primary opponent Leslie Crocker Snyder,......