I have the same problem on my 2020 GMC 3500HD . It just started leaking last week. The rear part of headliner was saturated. Haven’t had time to investigate yet , but did order a new seal for glass as it looked worn and partially detatched from the glass. It never has seated right. Always sat up a good 1/4 inch in the front and low un the back. I installed sunroofs in the dodge durangos in newark de plant for a good while and I know that job was overloaded. Is this maybe the culprit . Improper installation? Time study people ruin vehicles . Ill be trading this one in soon . Next one wont have a sunroof and possibly not a gm product as this was only one of many issues. Expensive issues. Steering box , exhaust manifold . Cameras not working properly.and now at all
