My 95 E320 wagon has 70k on it now, now problems. (It shouldn't) One thing I do quite frequently is clean the stainless steel rails which are exposed when the roof is open, clean those rails until they are shiny, and then lubricate with a light oil, like key oil or sewing machine oil. Also, tighten screws in the steel sliders because they can stick up and cause a jam. Lube the inner portions of the tracks and also the pop-up wind deflector. Doing all this, plus making sure not to open roof when there is snow / ice should cause the roof to operate properly for a very long time. It is a strange sunroof design, though, with the motor in the back of the car and the cables running the length of the roof. But it is silent in operation.

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2002 Mercedes-Benz E320 4Matic
1995 Mercedes-Benz E320 Wagon
2005 Land Rover LR3 V8 SE
1999 Audi A8 4.2L quattro