luckily i dont get any water inside the cabin of my car, the boot is another story.
Half way through winter i could open that up as the victorian wet and wild!! checked all seals grommits, even resealed the quarter windows just in case, nothing has worked yet...
to the OP, you could section off seals, grommits, parts and panels of the car with a tarp or something and get the hose on it to try and find the general area in which the water is coming in. Either that or as someone else said, try and find if its a common problem with that model, would save you a bit of time, im sure there is a Mitsubishi forum, obviously wont be as good and helpful as this one though they might know something haha
good luck finding and fixing the problem!