If it helps anybody else, here goes:-
Remove the seat height adjustment lever, I couldn'y find any catches to release so released it by easing with a large flat bladed screwdriver applied between the cushion and frame.
Remove the side trim. There is a torx screw at the front accessible from under the seat, the centre has a clip which pulls off. At the back, unclip the elastic which holds the curved trim which is part of the seat backrest, ease the sides out from the plastic end covers. If you look under the seat from the back you can see the attachment points for the elastic. There is one more torx screw for the side trim at the back.
The edges of the seat cushion are held down by plastic channel type clips. Squash the seat cushion to take some pressure off the clips and starting at one end unclip each side and the front. The is also a small section of clip at the rear of the seat.
If you're fitting a new cushion you need to cut away sections of foam on the outside (door) edge. These are pre-marked, one for the height adjustment lever, and two for the fixing of the side trim. Offer the trim up to the cushion to see which ones.
Fitting the new cushion is the reverse of the above. The pre-molded foam means the cushion locates in the correct position. Attach the clips around the side, front and back, squashing the cushion as you go makes this easier. Refit the side trim and lever. The most awkward part I found was the screw at the front of the side trim. I removed the underseat tray to give better access.
- ease the adjustment lever off with a screwdriver
- you may come across hog rings that need removing
- the C3 seat cover partially removed
- channel clip on seat rear section
