M-B does offer a complex grease specifically for the sun roof - # 001 989 14 51 (approx. $20). Unfortunately, its not packaged for single use applications; one tub will last a very long time. As such, its typically a special order item, which may explain why the dealer offered you brake pad paste instead.
The SR grease is a lighter weight than the brake pad paste and being light tan colored is less noticeable than the paste's dark green.