Any luck with this? I'm having the same issue with mine and I'm stumped. I noticed the same issue on the drivers side of one I looked at before I bought mine. The dealer was surprised when I pointed out how the floor mat and foam underneath were soaked completely through and squishy. My guess is it's a bad piece of weather strip somewhere or a clogged drain or vent. I've had the clogged ac drain line on a different vehicle that was flooding my floor but this issue is definitely related to when it rains out.