One problem we have come across on our fleet of 11 Z550EX side by sides is the seat inserts ripping out with larger than normal clients or it might just be a crap design  .

You will need;
4 x M6 washers with large outer diameter
4 x pan head screws M6 x 40 (cut down to size once in)
4 x M6 nylok nuts
4 x original washers.

Press the inserts back into the plastic 'wedges', obviously these would pull straight out if left that way

Grind away about 4mm of plastic and insert from the thin end upper surface so a screw head will clear the seat frame.

Cut away a little from the sides of 2 washers so the fit into the recess at the thick end. screw in the pan head screws until tight and then make sure the rear one clears on a flat surface.


Just a crude drawing to show what I did, (you WILL get used to these)