Hi Stuart.
I've just fixed that very same problem on my Clio 51 plate.
Had a very wet passenger foot-well!
To my embarrasment, I actually ended up doing it twice in a month. The first time I used an exterior sealant from B&Q which goes on white but dries translucent. Waste of time! It wouldn't dry properly. When it rained it turned white and ended up running all over the roof! Took me ages to remove it. Could have been the sealant was not suitvale ie. not waterproof but it said exterior, so go figure! I'd say avoid it.
Anyway, I ended up buying a product off ebay but it is available in a few places on the net. It's a black butyl 6mm strip. Cost about £15 for about 6 mtrs. Did the job perfectly. Will never leak again. The original strip under the plastic trim of the sunroof is spongy and i think age and the weather takes it toll. It was infact a car wash that exposed my failing seal.
You need to remove the sunroof glass, visors, interior light, roof handle, A- post trim, top of the door seals. All this to drop the headlining down a bit so you can get in and undo the many star (torx) screws holding the sunroof in place. I did start to undo more interior trim to drop the headlining fully but gave up and found it wasn't absolutely necessary. You can't help but bend the headlining slightly when undoing the bolts at the back of the sunroof but it springs back fine when you're done.
Remove all of the old knackered strip from the sunroof's upper trim and apply the butyl strip to the trim, not the roof. Don't put it on the outer edge of the trim neither or it will bulge out when you tighten everything back up and you'll have to trim off loads of excess. Try to apply it about a few mm from the edge to give that bit of bulging room, if you know what i mean. It's sticky, pliable stuff so try and do it in one go and don't fiddle about with it too much.
I think that's it really. Plan a whole day to do it so you don't rush it but you can do it in a few hours is pushed.
Hope that helps.
John, March 2008