My S is 4 1/2 years old and I've recently noticed that the interior is very damp. The car seems very well sealed (no water inside after washing or rain) so I'm lost as to what, exactly, is happening. Any thoughts?

 

I would try check the trunk under the tool kit area.. to see if its damp there. I've had water stuck back there before... due to throwing wet gear back there and it made the whole cabin damp and muggy.

 

Welcome to S2ki btw.

 

Do you have a slimy film on the inside of your windshield? If so, you might have a leak in you heater core or the hoses going to it.

And Welcome!