The two most common areas I have found where water comes through the bulkhead are (a) the dash vents, and (b) the plastic panel covering the the large, irregular shaped hole where the wiring loom, speedo cable, etc, pass.
The dash vent has a foam rubber gasket behind it, which, if properly fitting, should seal on the raised lip of the bulhead. Over time, the adhesive on the gasket lets it slip down, and though it still looks OK, it isn't being "squashed" between the vent flap and the raised rib. I know this is the case on mine. I just haven't gotten ambitious enough to fix it yet.
By the way, the water is actually running down the inside of the bulkhead, in front of the dash panels. (in either of the a. and b. senarios) I sealed the plastic pice with some silicone sealant