Leaking Rear Quarter Windows

Has anybody had this problem. I have 94gt, has been leaking during the last rain.
Water had got inside the trunk, however, the trunk gasket is good. Now I also found water/ moisture on the rear seat arm-rests (molded into quarter panel). I believe that the quarter windows and/ or rear windshild may be leaking. I'm sure this couldn't be a common problem with our cars, I have not heard of this before.
Has anybody had this problem? If so, where was the leak & what's the fix (w/o removing the glass? if possible?

I actually did try to spray it down & check for leaks, however, I didn't find the source of the leak(s) and I was by myself. I Will get someone to help, very cumbersome to do alone. Can't figure out why, All of a Sudden, I got a Leaky Car. Thanks for the Advice!