W639 rear 2+1 seat issue

[movastar]

Hi I have a w639 115cd compact , 58 plate. I am having an issue with the double seat of the 2+1. The middle seat won't release to fold flat. Therefore it won't allow the double seat to tilt forwards. The lever between the seats that releases the back mo es but feels as though its not connected to any thing. Its difficult to see the mechanism as its buried in the seat. Any help or tips would be gratefully recieved. Its a major inconvenience right now. Thanks in advance. Martin