I recently noticed moisture inside the vehicle on the past few cool days. No odor or visible obvious leaks, but the carpeting under the rear passenger side floor mat was very wet. I wet-vacuumed the carpet and it quickly dried out in the heat. Again I noticed damp carpeting after a rain storm when the car had not been driven. Does anyone have any suggestions as where to look for a blocked drain, leak etc.? Thanks.

 

Since it is the passenger rear floor board I would look at the sunroof drains. The rubber around the sunroof is a water deflector and not a waterproof seal.
There are drains in the channel at all 4 corners they have hoses that run down thru the vertical pillars and thru the bottom of the car.

 

One thing to keep in mind is, water takes the least path of resistance. So that being said, I start with the simplest possible paths to that point. Rolled door seal, window guide seal, holes drilled in the roof from a ticked off neighbor because you own a Jag ....check the carpet for a trail to that point of settlement.

 

Last week I checked all four drains around the sunroof. The forward driver's side drained a little slowly and the other three sucked the water down rapidly and drained under the car. With additional hot water, the sluggish one opened up. I dried car out and parked it outside all weekend. Fortunately it rained...damp carpet under the front passenger seat and rear passenger floor again. Are there drains around the firewall/windscreen that could be plugged?

 

There is a drain beneath the plastic cowl panel on the right and left corners just in front of the windshield. You should be able to check them with the cowl panel in place. If one is plugged you will need to remove the panel.

 

In my experience with a 2001 XJ8, it was a disconnected drain tube from the air conditioning system. It is accessible from underneath the dash on the passenger side and water tends to drain to the right rear. At first I was mystified as to source, but that was it. If you have not been running your system, then I am not so sure. But it was definitely the source of my water. Thirty minute fix. Not so fast with the carpet which I had pulled up and completely dried to avoid mold and odor.

Hope that helps.