1999 AUDI A8 Power Train Problems

MINE IS A WELL-MAINTAINED, NEAR-PRISTINE, LOW-MILEAGE CAR. WITHOUT WARNING OR PRIOR INDICATION OF A PROBLEM, THE TRANSMISSION SUDDENLY CEASED TO OPERATE CORRECTLY WHILE TRAVELING ON A BUSY, FOUR-LANE URBAN HIGHWAY. IT RESULTED IN THE CAR HAVING LIMITED FORWARD MOTION, POOR CONTROL, AND VASTLY DIMINISHED POWER, MAKING IT EXTREMELY DIFFICULT TO MANEUVER IN TRAFFIC. I NARROWLY AVOIDED A COLLISION WITH OTHER CARS. I MANAGED TO DRIVE THE CAR BACK ABOUT 20 MILES TO MY RESIDENCE IN THE LIMP-HOME MODE--ONE FORWARD GEAR, THE ENGINE REVVING BETWEEN 3000 TO 5000 RPM'S WITH THE FORWARD SPEED NO MORE THAN 35 MPH. I PARKED THE CAR AND LEFT IT FOR A WEEK WHILE TRAVELING. WHEN I RETURNED IT WOULD NOT MOVE IN ANY GEAR. I HAD IT TOWED ON A FLAT-BED TRUCK TO AN AUDI DEALER. THE PROBLEM WAS DIAGNOSED AS AN INOPERABLE, UNREPAIRABLE TRANSMISSION BROUGHT ABOUT WHEN "A BOLT SEPARATED FROM THE TRANSMISSION HOUSING...