How do you repair the rear windscreen wiper on a Fiat Punto Mk1?

If the blade is worn out...the answer is a whole new wiper arm. These can be got from Fiat dealers...or usually from Ebay for a fraction of the dealer price. Swapping them is simply a case of lifting the cover on the old one, where the wiper is attached to the car, undoing the bolt and slipping the old arm off....then fitting the new one in the reverse method of removal. Alternatively, what I prefer to do is to just change the rubber. If you buy an ordinary wiper blade of the same size or bigger, you can just take the rubber out, cut it down and slot it into the wiper arm. This way is much much cheaper, but involves a little more work. Replacing the arm is probably the most sensible option though if you want to be on the safe side.