Metal cips or green plastic tabs?
They changed sometime in 2010 I gather.
http://www.catcar.info/ford/?lang=en...ODg4OCsxMzM%3D
shows (9A317) a metal clip.
These potentially get weaker by over extension when installing.
Solution might be to bend them back a bit. They should be installed before the leak off pipe is pressed in.
Another idea is to cable tie them in as emergency backup.
I googled it out of interest, no problems with mine, plastic tabs.