107 Seat back slippage
 

Have an '87 560SL, and the driver's side seat back slowly slips back.

I can bring it forward by rolling the adjustor wheel on the side of the seatback, but it gradually slips back.

Is there any tension adjustment that can be made...anything that can be tightened to keep this from happening?

Have done a search, but found no answers. Would appreciate any advise. Thanks in advance.