how can I mend the rear wiper on my Peugeot 407?

The washer lets water down on to the rear screen, but the wiper doesn't even attempt to move. It felt quite stiff when I lifted it to look to see if it was anything obvious. I have only just acquired the car, so don't know if it was working previously.
My car is a '55 Peugeot 407SW hdi estate.