I had this problem about 2 months ago and took my C180 to a Benz dealer. I saw them applying this thick whitish "grease thing" all along the inside walls of the top because my sunroof moved very slowly and grudgingly. What was worse, it refused to tilt. It just stuck there until you gave it a sharp jerk from inside the car upwards and then it would go up. The next time it would stick again. A few repair shops said it would need a total overhaul...pull out the whole thing, replace all the faulty parts and those which will break when you pull it out and totalled about A$1200. After the grease job which cost me a few dollars only the sunroof is now in perfect order, does what you want it to do all the time up/down tilt, slide back and slide shut without fail!!! Sometimes, the Benz dealers are really more dependable and trustworthy. Cheers.