Ok, managed to get hold of some waterproof duct tape from a plumbing place.
I made a neat and tidy job of taping around the plastic seal and the metal roof, seemed good too.
Until it leaked the next day!
Looking at it more and actually having someone pour water on the sunroof and me sitting inside the car I've realised it's not coming from the seal I thought, it's like water collects between the glass and the seal, trickles into the corner and then just escapes through a hole and ends up on my roof lining.
I unplugged the drain tube and poured more water, it doesn't even go down it.
Does this sound like the hose could be blocked from the sunroof bit? (the plastic spout that attaches to the sunroof), or does it still sound like the seal (but the leak coming from the inside of the seal and not the outside like I first thought).
Took a pic, the red arrow is pointing to where the water comes down.