Mercedes-Benz 2001 M-Class Operator's Manual page 131

Instruments Instrument Technical
Operation Driving Practical hints Car care Index
and controls cluster display data
Interior equipment 128
To remove seat: 3. Move lever (5) upward and remove seat.
1. Lift tensioner (1) upward to a horizontal position to
release tension of the strap.
2. Disengage hook (2) and attach belt at hook and loop
strip on underside of seat.