Cadillac 2013 XTS Owner's Manual page 53

Keys, Doors, and Windows 2-25
Dirt and debris may collect on the
sunroof seal or in the track. This
could cause an issue with sunroof
operation or noise. It could also plug
the water drainage system.
Periodically open the sunroof and
remove any obstacles or loose
debris. Wipe the sunroof seal and
roof sealing area using a clean
cloth, mild soap, and water. Do not
remove grease from the sunroof.