If you do the soap thing, best wayt o do is use a large spray bottle filled with water and your favorite dish soap. Don't use alot of soap, just about a teaspoon in a quart of water. This is not a matter of having a tremendous amount of suds only a clear spray that develops bubbles if coming in contact with your air leak source. Kinda like blowing bubbles when you were a kid. Do as told, roll up windows, turn on a/c or heater fan, Temp does not matter just volume of air, shut doors and and start to spray the water/soap solution in areas that is suspect. You'll need to spray with a mist not a stream. Spray untill area is wet then move to the next. Focus on seams and joints along windows and doors then move to the firewall and dash area. You may need to take out the vent covers in the area of the wipers and spray in there. THe water getting in may be wicking from another area so don't concentrate too much in an obvious area. Do windshield top and sides, do the area ofthe roof racks, you may have a bad weld and so on.. If the solution sparyed on starts to bubble, wel then you may have found your leak. Especially if is in a strange area like not around vents and such.. Good luck.. Remember of you use dish soap, you'll need to wax your car again as it'll strip the previous wax off.