My old 2007 Fiesta suffered a serious failure of the off side front suspension arm.   The car has about 117K miles and is in generally very good condition for the age.  I gave it to my daughter and son in law last year as a run-around.  My son in law was travelling at about 10 MPH in his work car park when the forward hinge point on the arm completely failed, causing the arm to separate from the bush, which remained bolted in place.  This allowing the wheel to move backwards, ripping the inner drive shaft joint apart.  It had passed the MOT a few weeks before.  The failure appears to be due to corrosion on the side of the joint which is hidden from view inside the socket in the chassis which the arm is bolted to.

Fortunately this didn't happen on the open road but the bodywork was damaged by the wheel moving around when it was dragged onto the recovery vehicle.  Obviously could have been far worse.  My local Ford dealer says they have never seen this before. 

 

 

Honestly from the amount of visible corrosion on the part a tester should be able to see, it shouldn't have passed, I can see from the pictures that the metal looks paper thin all the way around.

It's done well to have what looks like an original arm after all this time!

I replaced my arms with Moog units maybe 5 years ago and they're still as clean and shiny as the day I fitted them.