On Tue, 15 Dec 2009 13:23:50 -0800, Michael D wrote:
Theres a ledge on the outside of the window frame, about 3 inches
wide which runs the length of the outside window frame (see the
photos). Its just above where the water gets €“ is the most likely
suspect?

I'd certainly start with that; as a very cheap test, seal along the join
with some sealant and see if the problem goes away (nowt wrong with it as
a more permanent solution either, but you'd be better off stripping all
that flaking paint off, re-painting and then sealing afterwards if so)

Any experience of whats the most likely suspect or suggestions for
tracking it down would be much appreciated.

If the above doesn't help, it might be worth noting what the wind
speed / direction is whenever it does happen - maybe that'll give a clue
as the source...