[Solid Snake]

I have done searches on the forums for this problem, but I think mine is a bit unique so I am starting a new thread.

I have a 87 Turbo with the Lindsey racing 300RWHP kit on it. So it has a 4" exhaust and no cat.
Also, the previous owner installed new shocks for the back glass and the frame for the glass is now bent pretty bad (a common problem it seems).
So the back glass was definitely leaking as I could hear wind noise. I am poor and not willing to risk breaking the back glass so I just filled the bent part with this silicon stuff, and even some tape to make sure it was sealed.

So if I have the windows down, or the A/C running, I smell exhaust in the cab pretty bad. And that is the unique part, if I have the fan running, but the A/C compressor off and the windows up, no smell at all. I am assuming that the A/C is creating a different pressure in the cab and sucking exhaust in from somewhere. Because if I stick my nose in the vents while the A/C is running I don't smell exhaust, but the cab is definitely full of exhaust And there in lies the problem. I can't seem to figure out where the leak is. I think it must still be coming from the back glass, and that is what I am afraid of because I don't really have a way to fix it, being broke and all.

Let me know what yall think,
Thanks!