I had the prob on a ph2 clio, so was a bit tougher. (i've just noticed you have a ph-1, ariel at the front of the roof?)
You can't 'see' if its broken. it just breaks up inside, no doubt due to water/cold weather etc.
Just take the interior light off and unbolt it. Swap over.
ChrisD172... Good luck! lol!! (Ariel at the back? Roof lining has to come down!)