If you get a length of pipe like screen wash tube you can blow down, get some one to spray a soapy water mix on the outside of window whilst you blow down the pipe on the inside going round the window panel and watch for bubbles, shame don't still have it when I worked at rover ( total shit boxes ) we had a ultrasonic thing you put in the car and turned it on ( I don't mean talking smutty about micro processors) then with a sensing wand went round panels looking for sound likes obviously if it found anything it meant water could get in