ive been having almost the same issue - the soggy floorboards. But mine only leaks when it rains. My Bronco's an 84, so 29 years old this year? I pulled off the kick panels on both sides off and the access panels and YUCK!!!! Pine neddles, leafs, tree seed pods had been in there sssooo long that I had soil in the cowel drain holes. There was so much crap that it was up to the bottom of the acess hole & after I cleaned it out I could fit my whole hand down in there.

Moral: clean those cowel drain holes. lol