cyclical

Of course its from that windowover the cab, next to the bed, dry rot under there shows me It was a problem from before I bought it,...of course, but I have looked at the seal and it seems water tight. Still there is allways a full window well after the rain(in Portland this is every day now) and I bet this is a common problem. Just about half of the used Toyotas with the big window in the front had dry rot/past leak evidence,..in the SAME PLACE..It's always under the bed at the low corner...