I had the very same problem this week in my 85 Westy. Took the PS-door panel apart and poured water over the window and door and inspected inside with a flashlight to find where drip is. On mine, the water comes in between the P-side window outside weather seal, which is really cracked (the black rubber one that covers the chrome strip). As the water was streaming down the inside of my door it soaked my speaker (mounted top fromt of door panel) thoroughly....ugh!