Had the same issue with a 2015 Sierra Denali pickup a couple years ago and had to replace the gasket which was easy; and had another leak under the antenna module on the roof over the driver side. It throws all kinds of radio errors on a scanner. Now, torque converter issues. Traded it in today for a 2020 Navigator (because I never got my 12 ft Hobie Pro in the water this past season). Lifestyle changes
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Can't live with them, can't live without them...