Cabin Leak-1989 Lincoln TownCar

I have a 1989 Lincoln Town Car. I’m from North Carolina where it hasn’t rained for months. I bought this car about a month ago. The other day, it FINALLY rained for about 4 days and now I’m noticing a sour smell inside the cabin of the vehicle. I’ve traced the source of the smell to a wet spot on the front right corner under the dash where the carpet is wet. What would be the best place to look or what is the best way for me to find out how water is getting inside so I can put a stop to this? Any help would be great! Thanks in advance!

Start by checking the AC drain tube, which is on the firewall, low on the passenger side. If the drain is clogged water from the AC evaporator, or rain water, cannot drain out of the ventilation system and will instead leak onto the carpet.