Yeah it's pretty common unfortunately! From what I've read, the problem usually lies with the seal under the windshield frame (bad gasket or windshield frame itself rusting out) or a clogged drain tube in the cowl vent. You can see the drain tube on the firewall when looking from the front of the jeep.
View attachment 2796577
I didn't pull it off so I'm not sure how it's attached, but they say you need to pull the tube off and clean it out because it gets clogged with dirt and other waste from the rats and causes water to back up and enter the cab through the vent holes. The vents are on either side of the cowl opening and open directly to the inside of the jeep. The picture is an example of one of the two vents on either side.
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I took the pic from inside the dash and you can see that there's a huge opening that lets water, wind, snow, whatever to get right inside when the valves aren't closed.