Marshall,  I confirmed by gasket failure and the compression gas in the
coolant with an "block tester"... you can get one of these at NAPA.  For
those unfamiliar- It is a glass tube with a rubber squeeze ball at one and a
rubber intake at the other.  You hold it in the coolant reservoir (after
removing enough coolant to keep the coolant out of the tester).  The green
fluid turns yellow if combustion gas is present.  Although I did not try this
I was told that I could isolate the failed seal by removing one spark plug at
a time until you get a clean test.  I didn't try this because I was skeptical
that once the gas is present I would not expect to get a clean test unless I
changed the coolant.  Maybe this is not true?  But the most compelling reason
for my not bothering with further testing is because you would not want to
reseal just one side of the engine anyway.  If you have a failure you need to
do both sides. Im not a professional mechanic (I just like to get in over my
head on my own cars) but Im told there are reliability and performance
reasons for doing both sides.  Maybe someone could elaborate on this.

Eric Small
So.Portland, Maine
'86 GL Weekender