I was looking on the passenger side, i try it on monday again. ThanksThe parts diagram shows a drain cover part number 3035981 for an '87. However when I look in parts section 2.11 I don't see that listed for a '87. Your guess is as good as mine which is valid. I can't find a picture of the part.
That is a clam shell cover with a top and bottom half. The parts diagram shows the drain cover near the firewall about in the middle or toward the drivers side. If it has a cover it may be blocked. I'm surprised that you can't see it from under the vehicle or feel it from above.
Removing the top half of the cover may be possible but I bet that would be a PITA. Removing the top half may give you some access to find the drain.
The black gummy stuff is called cork tape if you need some. NAPA or other parts stores sell that in rolls. Removing the top would give you a chance to clean the evaporator core too.