The driver side wiper arm underneath (bonnet) has somehow de-attached itself to the driver side (metal) wiper arm, so 2 in 5 times or thereabouts I have to stop and reattach it as it unclips itself. Think it just needs a rubber washer to hold it in.

If anyone has experienced this and has ideas how to fix,
it would be much appreciated!

Common fault. Good news is you have lots of options. Buy a complete wiper assembly from Fiat ( ahem), Buy upgraded wiper link arms from Wipex about £25 inc p&p , turn the link arms the other way around and get the last bit from the rubber , weld or glue a washer at the end of the ball joint to stop the arms falling off or lastly keep fitting clever combinations of cable ties and rubber bands that will fall off as soon as the rain gets really serious on a motorway.
I have used the Wipex and they are good , not everlasting. Take the assembly out of the car and clean all traces of rust from the ball joints to give the new bush a better chance of lasting if you decide to go that way.

I have 2 puntos fixed the first one by turning the arm over and the second one by stealing on of my other half's hair clips both of which have done a Stirling job

many thanks for all your suggestions! a great help! :¬)

gonna try placing the arm above to start. let you know how I get on.

i welded washers under both balls.works a treat.

when the snow fell we were overwhelmed with wipers breaking,we removed them from car and drilled all rods and put a screw and washer into the ball nipped up to allow movement and rotation off arms still there years later
note wipers are not tools for removing snow from windows