So here's latest and the greatest.
We had absolute crapstorm for weather, TN type downpours. For days. After driving to work and parking, I checked on the carpet again. Well, damn me, same wet spot on the mat, as before and same wet spot in the carpet underneath it.
But, this time, I took deep breath and close look at the OEM floor mat backing. The rubber piece with dimples in it.
To my surprise, there was TWO wet spots. Quick look at the fabric side of the mat showed that, the second wet spot was exactly where my left heel rests.
Mat backing showed 2 spots, one, larger, under the right heel and smaller one, under the left heel. As I move left leg and the right foot, because of the gas pedal, is mostly in the same position.
Two round spots, with NO streaks to them, that would point towards some side leaks from the firewall or driveshaft well.
Perfectly localized. I did shine bright light before through the mat carpet, and saw no holes in it but, this time, I folded mat tight over the wet spot and saw small pinholes that, actually, were there. They showed only when rubber backing was stretched by folding the mat.
Considering that there is NO damp carpet anywhere around the wet carpet spots, I am pretty sure, it is water seeping through the mat from my shoes.
I feel sorry for the guy, bless his heart, who replaced the windshield, on his dime, apparently, for nothing. Bless his heart, what a guy!
Off to Walmart, to get floor mats.