Welcome to the forum. You'll probably want to clean it up really good and lube the sliding parts. The trick is to use only the Mercedes-Benz lubricant. The dealer will sell something like a 1 pound tub for a ridiculously high price, but smaller quantities are available from other sources. The best thing to do is make use of the "search" function at the top right corner of the page, and search for "sunroof lube."

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References