Don't know if the same...
Al, on my '96 S500 Coupe, the seat backs lock into position anytime the car is running or the ignition is on. When the ignition is off, the seat back can be tilted forwarded.
To get in or out of the back seat when the car is running, there is a button release on the side of the seat backs. Its obvious and doubtful you could have missed it, so maybe it was a change in '97?
Because the default condition (engine off) is to release the seat back, you may have a relay stuck or something else that's locking the seats even when the engine is off and the key is out.
Sorry not of more help.