Cowl/Firewall leaking

[FlatBlack65]

I have an issue with water making its way down the passenger side behind the side panel under the dash somewhere. I am going to seal it all up as best as i can, and as far as i can reach to get sealer in there (it's a '65 that runs and is complete, with nothing taken out under the dash except for some old AC ducting i no longer need)so i don't have access to the whole area up in there (fender/firewall/sidepanel/dash junction). I was thinking that if i pour some water down through the cowl vent below the windshield, it would leak down and show me where the water is making its way in. BUT, I really do NOT want to pour any water down in there and cause moisture to be in that area. It hasn't rained in a couple weeks. Its only around 40-50 degrees during the days, so water drying up completely in those joints will take probably weeks. So, to do the "leak test" and not have water up in there, is it a good idea to use rubbing alcohol? So that it will evaporate quickly on its own, but still show me where the leak is as its dripping down?

[FlatBlack65]