Finding windshield leaks with baby powder

Hi all,

I heard about a way to find windhsield leaks between the glass and the rubber by putting baby powder on the outside at the junction between the rubber and the glass. Compressed air is then directed at the windshield on the inside of the car at the junction between the rubber and the glass. Anyplace where the powder is blown away is a place where there is a leak. I wonder if this would work to find a leak between the rubber and the car metal? Maybe a leaf blower used inside the car would work to force the air around finishers inside the car? Anyone else heard of ideas on finding leaks around the windshield? I want to be sure my car doesn't leak as an anti rust measure.

Mike