Hello everyone, its been a while since I have posted. I am still working on my 87 convertable. I have just finished taking a door from an 89 2-door and modifying it so that it fits my 87 convertable. I also had to replace the drivers floor pan which I also got from an 89, it fit perfectly. I even took the 2.8 from the 89.

So to find out where the water was coming in from, I ran a hose on the windshield. Well water just poured into the interior. So after cleaning up the mess, I pulled the cover from the plenium and also the two plastic shields covering the vents. The chamber itself, the metal was in good shape. A few places needed seam repair. the water was coming in from the fan housing. Underneath the plastic cover on the passenger side there is a "well" where the fan resides. At the bottom of that well there is a drain hose which was blocked up. Unblock it and the water runs out fine. The outlet to the hose is at the end of the steering rack.

On the driver's side, there was just a flap which was not plugged on my car.

If you have water leak coming in from the firewall, I suggest you check this.

Hope this post is useful to someone.

this is a well know issue and quite common. iirc, there is a how to in the 2nd gen section