How are the rubber seals around your windscreen. If they are dried out and cracked, water can get in and tends to pool in the corners of the windscreen on the inside on top of and below the dash crash pad.
How is the seal at the bottom of the windscreen between the body and the screen? Again, if it is dried out, driving at speed you may get some water under this seal that accumulates in the corner and drops down the holes on either side where the windscreen posts drop down.
How are your two seals that run up the side of the windscreen? I find that quite a bit of water can get into the cockpit from there as well if these seals are not in good shape.
Lots of other areas as well but those seals would be a good place to start.
Cheers,
M. Pied Lourd