My guess could be that you have a problem with the plastic cuver at the windscreen.

When not all the water is routed as suppoost, it could run behind the cuver, and streams along the firewall.

One the picture you could see how the water should leave.

On the other you could see were water is going, when its routed behind the windscreen trim

There is a trim along the window, an big cover on top, en a cover where the filters zitting in. No other parts.
If you feel on the edges on the topcover and window trim, you could feel that it’s a bit soft. If that hardens out you could easy get on wanted gaps.

Hope it’s of some help

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