I have a situation where my 90 vanagon, after running for a few miles
began to exhibit "cooling system problems":
The temp needle went to the top and the red light began to flash. I
drove a little while longer and idled downhill home.
Coolant was leaking out of the (it looks like top of )  pressurized
coolant reservoir and as well as being under what looks like higher
pressure than normal. The car did not appear to be overheating. After I
stopped the engine I could hear pressure noises (what sounded like fluid
shifting around as the engine cooled off)

Does this point definitively to a head gasket leak? If not what are the
other possibilities?  My coolant reservoir  had signs of leakage around
the top where the sensor fits into it prior to this and this was pointed
out to me by a mechanic.

Thanks !  -john