Well, after a very quite several months my head is leaking....again.  I'm
rather frustrated by this recurring problem and am wondering if either I am
doing something wrong (very likely) or if there is some other problem (also
very likely).  Here is the background for anyone who is able to offer me
some guidance:
- Van is an '85 GL 1.9L with 120K
- Bought van used at 65K.  Heads looked recently resealed as the sealant
goop oozing out from around the rubber looked pretty clean and new
- At 85K the water pump bearings blew on the interstate and I wasn't
circulating H20 other than out the back of the van.  Replaced water pump
road side and drove 400 miles home with a plugged/melted CAT that created
excessive back pressure.  My stupidity in driving the van without hacksawing
off the CAT or the prior overheating resulted in a blown compression seal
that was pressurizing the coolant with engine gases so I replaced both head
gaskets, again this was at 85K
- At 100K I started getting engine gas pressurized coolant again and pulled
the left head first where I found coolant inside the back left cylinder (#4?
I think).  Anyway, to save time and money I replaced only the left head
gasket and didn't touch the right figuring that the coolant told me where
the problem was.  I was correct and that fixed the problem.
- At 108K same damn problem.  I pulled both heads, had them rebuilt, checked
for cracks and flatness and everything checked out perfectly.  Back on they
went with new gaskets.  Problem solved.
-Now, I'm at 120K and the other morning my heater starts blowing
cold/hot/cold/hot and temp gauge is fluctuating.  Take a look at
coolant....same darn problem, it's getting pressurized by the engine gases
again.

Each reseal I took extra special care to torque head bolts exactly per spec.
Last time I even let the van run for a day or two and then went back in to
retorque just in case.  Any suggestions?  I feel that maybe driving with the
melted CAT plugging my exhaust did me in, but nothing appears to be wrong
with the heads.  Also, I'm betting 100 to 1 it's the left side again.  Why
always that one stupid head?  Can I retorque or extra torque the heads now,
12K after the last reseal in hopes of stopping the leak?

Any help, mechanical or spiritual, is greatly appreciated.

Thanks,

Mark