You could try to clear the drain tubes by running some wire such as trimmer line through them from the top down. There are also two drains near the front windshield cowel on the left and right hand side. Make sure there are no obvious obstructions such as leaves, twigs etc. Depending on how when the carpet is getting you could also consider a faulty evaporator drain if you have been using the A/C a lot recently. Those two drains come down next to the transmission tunnel and exit underneath the car.

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1989 300CE