Warrior Leaks
Some years ago we had the same problem with an Archer, couldn't find the source for months. The lock on the crew door had always been slightly loose. The lock was eventually replaced. When the panel was removed from the door to change the lock clear signs were evident that water was entering around the lock running down the interior of the door and collecting on the floor behind the front seats. The door window is also often ignored when looking for leaks, once again the tell tale signs will be hidden within the door panel.
Worth checking!