If dripping off dash when raining it could be blocked water drains in channel infront of windscreen.
Pour water into area and see what happens.
Could also be windscreen leak.
Pour water down sides of screen while someone watches inside. Then try top of screen.
Feel ontop of roof lining with fingers where it meets screen. If top of screen is leaking water can collect here and run to one side and down windscreen pillar then off the bottom of dash.
Will need screen resealing if this is source of leak.
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March 2011