Hi thanks for answering so quick but whatever might get blocked, surely any overflow water should just drain back into the engine compartment. As far as I would think, there shouldn't actually be any way where water could get past the bulkhead into the inside. It should be sealed apart from wiring and pipes etc passing through. After all you wouldn't want fumes and stuff winging their way through 'Holes' in the bulkhead. But also thinking about your suggestion, the only other thing i can think of is that where the air intake is, when water gets in there which it must do because of it being there under the windscreen, if any drainholes do get blocked that must mean that any collection of water in that area would mean that the water might get into the inside through the heater air filter. If so how to get to the necessary drain holes for cleaning? John the Handyman.