OK, further my previous answer. I've now replaced the wiper arm with one I got from a breakers yard for a fiver (lucky me - it was his last one!) but what I did do before I fitted it, was compare it with the old one.
It looks as though what has happened is that the bearings in the arm have gone, which created the give for the spring in the arm to put pressure in the wrong place and bring the metal parts into contact with each other, thus wearing the arm away, creating more room for play, putting more pressure on the bearing. Basically a vicious circle. At some point, I would have thought the bearing would give completely and the whole arm fall apart!
In answer to the original question, can it be tightened up - If you have the same failure as me, then no, unless the bearing can be refurbished, but I still think your best bet is to get to a breakers yard and hope they have one in, else the main dealer will fleece you for a new one! BTW, I went to French Spares in Ranskill, nr Retford, Notts, only because it's local! Luckily they are a specialist Peugeot/Citroen/Renault breakers, so do get newer model cars with accident damage as opposed to the older end-of-life junked models!
Good luck
Tony
Tony Corbett, September 2008