Maybe a bit more history is needed?
Is this a new to you motor with a pre-existing problem or has it just suddenly started leaking?
If it's just started leaking, can you think of anything that has changed?
Have you tried drying it out, then jet washing it in various places until it leaks?
It may sound daft, but have you had a windscreen replacement? I heard some story about autoglass having a bunch of screens which had the fitting markers in slightly the wrong place which meant they would end up leaking but it's not an obvious place to check.