@gothitjulie, did you find the source of your problem with rainwater that gushes out when the driver’s door is opened?
We have a 66 plate SEAT Alhambra and have recently noticed a problem that sounds very similar. In our case the water appears to be not inside the door, but trapped between the upper and lower rubber seals so that it sloshes out when the door is opened. It seems to happen on the driver’s side only. We’ve noticed this in the past few weeks but, since we’ve had the car only a few months, are not sure whether this is a new problem or whether it’s always done it and we’ve just not noticed it before.