I'd think the headliner would have to come out.

I'd have a helper spray the car with a hose in various areas until you see where the leak starts. You might find out it's not what you think... like I did

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.