After some Rain

My Duster got stuck in a little rain storm only for a small time,
and my brother noticed some water on the drivers side floor mat!!
He did'nt drive the car and the windows were closed and he found
nothing visibly leaking. Could it be seeping around the cowl, I never
noticed it before, but I never had it out in the rain when the car was out
here in Calif. The car has no A/C I wonder if its coming through a vent?
Any other suggestions to look for??