C Class Sports Coupe - Broken sunroof/part flying off car!

Just bought a great 02 Merc C Class Sports Coupe with a great spec and the panoramic sunroof.

Once I returned home I opened the sunroof using the switch. Everything was fine. Whilst it was closing, it stopped just past halfway and sort of jammed. I pressed the close button again and I heard a snap and a something fly over the windscreen. After closer inspection, a few metres in front of the car was a piece of plastic which I've uploaded.

The roof is closed, but it seems one side of the roof is sealed and tight, whilst the other side exposes a few hinges. It will only open a few inches now and I get that jamming/cracking noise.

Please take a look at the photos and let me know if you've got any ideas as to what the problem is. The dealers were good although weren't too happy as they are adamant everything was working. They asked me to take it back on Monday so they can investigate and said that we'll discuss the next steps after the problem is diagnosed.

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