Passenger footwell leak

I have a 2004 uk ford galaxy. It has a rain leak into the passenger foot well. I can see it dripping from the underside of the fan blower assy (see pic taken from under the glove box).  I've determined with tissue paper that its coming from the bottom of the blower flange, not running around the edge. There is a peculiar corrugation on the chassis metal work with a pitch of about 15mm and a depth of 6mm and I wonder if this is an intentional drain point in case water gets into the fan assy.

I've had the wiper cover guard out and cleaned all leaves, etc. out from around the intake, it's never had a pollen filter fitted.  When I run the hose on the windscreen I can't see it entering the air intake and it looks like it's draining OK.   

Has anyone come across similar and know the cause? 

Does anyone know if this is an intentional drain although that would be odd discharging into the footwell?  (unless it's a case of better in the footwell that filling up the blower assy) .  I have considered sealing it but I'm hesitant in case I trap water in the blower assy.