Actually you don't need new metal clips if you are careful!. I use a largish (500mm) F clamp to squeeze the clip from the back of the strut to the outside of the brake disc (with protective wooden packing block). Gently increase pressure until you can slide the 'hook' part of the clip vertically off it's catch point. As above ensure back of strut is clean as a whistle, then replace the return (again use the genuine Citroen ones - the GSF are total crap) and reverse the procedure though you may use a 'pincer' or 'crimper' to hook the metal 'catch' back together. Generally I've been able to slide them back with a pair of screwdrivers.
Proviso is do not over pressure the clamp as that may damage the strut. I must have used this technique at least 6 or 7 times and never had to replace a clip or had a leak from the seating area, except once with a GSF return....

and btw that did not even do a year before it disintegrated, incorrect material.