Car is back in the driveway.  Taxi Guy drained the transmission and torque convertor, then added 12 quarts of MerconV fluid.  He drove it around, then added a 13th quart.  I didn't have time to hit the highway on the way home, so I don't know if this sloved the chatter issue yet.  Will know within a couple of days...
As a side note, Vic now has 138,389 miles on the odometer.