How do I find rain leak?

That is always a fun job, its a bitch. But anyway you are looking for bad seals around the doors, sunroof, trunk seal. The most effective way of finding these kinds of leaks is to do a smoke test, you bomb the inside of the car, trunk, just watch where it leaks from. I do not know the technique in doing this tho, I had to have mine done at the dealership.

Another suggestion. Turn the heater on full blast. Make sure the system is in the recirculation mode. Close all windows and moon roof. Does this vehicle have a sun....moon roof? Let the engine run for about 10 min you should have a positive pressure in the vehicle. Now with a cup of soapy water and a brush...go around a swab ALL windows door seals and especially that moon roof.

Bubbles forming Anywhere? There is where she leaks.