If I recall correctly, there is possibly a crack in the air box under the grille next to the wiper mechanism shaft.
Remove the passenger side corner piece of the wiper cowl, remove the screw, and apply a little silicone and re-install.
The hole for this screw sits directly above the air intake for the AC/heat ductwork box. This is a somewhat common area for these trucks to leak water into the cab.
If that's not it, you may need to remove the whole wiper cowl. There's a metal cover over that area that the factory uses seam sealer on; sometimes the sealer cracks or fails and will need to be re-done. Less common though.
Remove the passenger side corner piece of the wiper cowl, remove the screw, and apply a little silicone and re-install.
The hole for this screw sits directly above the air intake for the AC/heat ductwork box. This is a somewhat common area for these trucks to leak water into the cab.
If that's not it, you may need to remove the whole wiper cowl. There's a metal cover over that area that the factory uses seam sealer on; sometimes the sealer cracks or fails and will need to be re-done. Less common though.
