As jklingel said... start OUTSIDE:There is a window off to the side of where the leakage is.
Is it possible that is where the seepage is?
We also had a record rainfall this year.
If it's damaged then take it off no matter what (you don't want to breed mold)... and sure, poke around in there to see what's what. But the problem and solution is probably limited to the outside.Should I take off the drywall for that whole section...