Not to put a damper on an otherwise great wrench-bending session but,
how about a pin-hole leak in the upper (left side) radiator hose?

--PJ
'89 HookerCar, '02 e-blu 6-spd coupe

Hope it didn't freeze in your storage!

I have had several coolant leakage problems with my '87.

I had a frequent small pool of coolant at the right rear of the intake
manifold next to the head.  It was a small leak and no coolant showed up in
my oil, but occasionally you could smell the coolant.  I lived with it for
years until I removed the intake manifold and replaced the gasket.  I used
GM grey silicone on the gasket and tightened the bolts carefully (with
thread lube) and a little tighter than spec.  This job is a lot easier if
you have a very long T40? Torx wrench for the manifold bolts.  It solved
that problem which I have been told is very common in these cars.

I also replaced the vacuum operated valve in the rigid coolant line leading
to the heater.  The valve is used to stop coolant flow to the heater when
using the air conditioner.  It is a poorly made valve and I tried to repair
it but the cheap plastic valve is not available and I was unable to find a
replacement seal, so I bit my lip and purchased the complete dual tube
assembly from GM for way too much money.

There is a service letter regarding the low coolant light.
It is document ID #268592
the title is 'low coolant warning light may be caused by trapped air
#88-43-6B'
You should be able to get a copy of this letter from any good GM dealer.  I
do not have a URL for a GM knowledge base to access this type of service
letter on the web.  If someone knows how please post it here.  I did
purchase the spec clamps but they are just normal heavy duty worm screw
clamps.

I understand there is also a common leak from the water pump mounting
surface which is also fixable with a simple gaskets change.  I have noticed
some drops of coolant under the front of my engine but I will live with it
for a while.

I am inclined to think that the aluminum thermal expansion cycles are the
cause of most of these leaks and that the cure is a THIN layer of silicone
on both sides of the gaskets and a little extra torque when tightening
bolts.  I suggest tightening the bolts then letting them sit overnight to
let the gaskets and silicone to flow a bit and then retorquing them before
completing the job.  I am also a big believer in using a nevr-seize type
thread lubricant on the bolts to improve the clamping force.

It is nice to get all the little leaks fixed but it was a lot of work and
the air conditioning heater valve was very expensive.

Good luck,  YMMV