Hi, think I might be able to help you I had the exact same problem on my 2003 5 door mk2 renault clio managed to fix it last December.
Like you I tried the drainage pipes and they where clear after lifting the sunroof out and checking it all it all seemed fine, I was getting huge patches of water just above and under the sun visors on both sides. The problem was, the water was getting in under the plastic rim on the sunroof on the outside. So to fix this, I managed to find this really helpful video:
after taking the sunroof section off tear off the old demolished seal and give everything
a thorough wash and clean until you can wipe it with a paper towel and it is clean, you'll be surprised how much dirt and crap comes off of it.
For a replacement seal, I went to b&q and managed to find this gem (it comes in a cardboard box about 20x20x2cm just incase you need to find it in store):
For £5 this is so worth it.
when putting the new seal on, I teared the rubber seal in half to get two strips. I then put one strip on the plastic that I had taken off and then put another strip on the body of the car around the rim of the sunroof. so that when I bolted the sunroof frame back on there was a very tight seal. I'm happy to say, the inside of my car has survived a very wet British winter and is completely dry on the inside.
Hope this helped!