There was no retainer in the first place. This is the linkage that connects the wiper blade to the wiper motor on a Fiat Punto. It's just a push fit, with nothing to hold it on. As it wears, the linkage eventually falls apart, and the wipers stop working. Puntos are notorious for this. It's a simply awful piece of design. Fiat's solution is to sell a complete wiper motor and linkages (for about £250). My bodge was cheaper, and I have resolved never to buy a Fiat again. This car has only done 30k miles, and many things have gone wrong.
Here it is, if you are interested. ;)