Lubricate the tracks! I know two people who have had to replace the motors in their 190s because the motors burned out while trying to pull the sunroofs across poorly lubed tracks. Considering that your car is only ten years old, your sunroof probably still opens and closes with ease, unless the temperature is relatively low.

Lube it and you should be fine.

__________________
Ben

The MBs:
1976 300D (W115) - 330K and still going (sort of)
1991 300D 2.5 Turbo - Sold at 221K
1983 280SEL - Sold at 206K
1981 300SD - Sold at 232K