Leaking water beneath dash?

Hello,

It sounds like the leak is likely due to a bad sealant around the windshield, as it only leaks when raining.
Some of these early nineties GM vehicles have issue with the factory urethane, they have a tendency to leak. Cadillac actually had a TSB to address this issue.

To fix this issue is to remove the old seal, replace it with new one and use urethane to create a watertight seal.
Depending on the severity of the leak, sometimes windshield has to be removed and have the base cleaned and re-installed with new rubber seal and urethane sealant.

Please let know of any questions.
Thank you.

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