Did the elastic mat retrofit on my driver’s seat, which was getting a bit uncomfortable. It’s made a massive difference, but I wonder if BMW left these springs off the M Sport seat because they add a bit of HGV-style seat bounce. Might just be my imagination though! 
You can see here that the rearmost embedded plastic “spring” has snapped where it attaches to the seat frame.
You can see here that the rearmost embedded plastic “spring” has snapped where it attaches to the seat frame.
