Even the later models aren't immune to this issue. I have a 2009 model and had serious problems over a couple of years - i have a thread on this forum which i will update soon, along with a few other threads that might provide some useful feedback for people on here regarding other issues. We had a tree overhanging the hardstanding, which dropped sticky sap onto the car in the spring and leaves and sticky berries in the autumn - a pretty deadly combination as far as the sunroof drainage is concerned. We've since cut this tree down.
I first became aware of a problem whilst on holiday in North Wales. After a heavy downpour during the night there was over an inch of water sitting in the passenger footwell. Fortunately, the vinyl coating on the back of the carpet stops the water soaking through to the metal and electrical components below - but this will not be the case if the route the leaking water takes is behind the trim rather than along the outside: this will partly be dependent on the camber that the car is parked on. The North Wales dealer (Tyn Lon) said the way they resolved the issue was blowing air down the tubes, although another dealer suggested a far more expensive solution that involved removing the dash!
Here's what worked for me, without any disassembly whatosever. (Incidentally, i did initially remove the A-pillar trim to check there were no issues behind it; this is removed simply by peeling the rubber door seal back and then pulling the trim firmly from the top end). Over the course of a few days squeeze some washing up liquid down the drainage hole inside the sunroof well, followed by warm water (drain-clearing fluid might risk damaging plastics and rubbers as well as risking permanent staining). Do this slowly and carefully, otherwise the water will overflow the lip of the tray and enter the cabin. I used a 500ml mineral water bottle for this purpose, allowing the water to be directed in a controlled manner. This should help to loosen the dirt inside the tubes. Then use some tubing to blow air through the hole. I taped some rubber brake tubing on to a plastic WD-40 tube, which i fed into the hole and then sealed with blu-tac). If the blockage isn't too stubborn a battery operated tyre inflator might provide sufficient air pressure to remove the blockage. This worked for me several times. However, it obviously didn't completely remove the debris as the issue kept returning a few months later. On the last occasion i reached a stage where the blockage wouldn't clear, despite several attempts over the course of a few days during which i would pour more washing up liquid and warm water down. Then a moment of inspiration from my partner solved the issue in an instant! She brought out our drain unblocker, which i'd completely forgotten we had. These are quite cheap to buy, and this is the model that we have:
https://www.amazon.co.uk/DRAIN-BLAST...=drain+blaster. By cutting up a strip of plastic milk bottle to form a tapering tube to marry up with the aforementioned brake tube/WD40 tube contrivance, and then taping it at both ends with insulation tape, you have then brought down the diameter of the drain blaster to a size that will fit the sunroof drain hole. Well, i was gobsmacked by the result. After priming up the pump and then releasing the trigger the water came gushing out of the blocked drain at the first attempt, clearing it in an instant. Six months or so down the line i haven't had any recurrence of the issue, although before winter sets in i will check again that there are no blockages and if necessary repeat the procedure. I would also suggest regularly cleaning the rubber seal around the sunroof glass, and also the paintwork that it makes contact with, in order to minimise the water and dirt ingress past the sunroof in the first place.