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.