2008 Cadillac DTS

Have a relative back In New Jersey who says the carpet on the front passenger side where you put your feet is real damp. She said she took it to Cadillac last summer with the same problem and she thought it was fixed. The car is going back to dealer but I thought maybe some one has seen this before. I was thinking heater core but she says it is clear water.

My guess was heater core as well! Or a leaky windshield gasket.