Leaking walls

We live on the West coast where severe winter storms and strong wind and rain is common. Over the past few years, water has been leaking into the second storey brick cavity and getting into the house, wetting the carpets and damaging the hard plastered walls.
The water is definitely not getting into through the roof (flat Colourbond with flashed parapet walls) as there is no damage to the ceilings. We have tried everything to stop the leaks but have been unable to find the source. I should mention that there are rollershutters installed which stop the rain hitting the windows and doors.
Has anybody had a similar problem and managed to solve it?

You could try application of clear waterproofer on the brickwork

OK thanks for that. The walls are painted with two coats of a good quality acrylic paint but I will check to see if it's possible to paint the waterproofer over the paint and then apply another coat of paint over the top of that.