It briefly rained yesterday, a drizzle for about ten minutes in the early afternoon. My car sat parked the entire time. There were no puddles anywhere. Today, more than 24 dry hours later, I noticed that the carpet under my driver'* seat floor mat was wet.

I was able to lift the carpet enough to slide my hand underneath. There was thankfully no rust hole in the floor, but the carpet was soaked down to the metal.

I don't recall this happening before last fall, when I pulled up the bottom door trim to check my ground bus for corrosion (and it was spotless). I thought I pushed everything back into place, but what should I check? Everything looks fine.

I can't tell in your picture, do you have a sunroof?

No sunroof.

Pull the driver'* door trim panel off and look for a continuous seal all around the watershield (translucent plastic sheet) to sheet metal. Repair as required.

That watershield got torn years ago the last time I was in the door; I didn't realize that it had a function until well afterwards. However, it never used to leak until fairly recently.

Is there any way to fix it if it'* torn, say, pick up a roll at Advance?

In the 2000'* that seal is critical, in the 92-99'* not so much. I'd be looking at the trim piece over the doors for a crack. If that'* cracked, then look at the seal around the door, specifically the top. Likely your leaking there.