Before you start spending money and pulling lots of stuff apart ... well.
It may just be my chemo fog but your description seems too vague to really give you targeted feedback.
1) seals and gaskets shrink and distort over time. BUT, even with that, many aftermarket products won't fit or seal as well as even an aged gm part in some instances.
My questions would be:
1) are you hardtop, sunroof/astroroof, or ttop,
2) is there or has there been a vinyl landau roof/half top on the car?
3) can you give us a pic of where you're seeing the moisture, even if it's someone else's car you just take paint/photoshop, circle the wet spots with your finger, and repost it?
