New long block, coolant leak

I installed a new long block in my tow pig. I can't get it to run right even to break it in (only about three minutes of running so far).  Immediate coolant leak down the back of the right head.  Pressure test held 12 psi for 30 minutes.  I took the exhaust manifold off and inspected, couldn't find a leak.  Fired it again, now more drips and won't run right.  Look closely at cyl 6 (just left of center).  Plug is wet with coolant. 

I predict cyl 6 is leaking coolant.  Anybody think similar?

Cyl 4: 150 PSI

Cyl 6: 150 PSI

Cyl 8: 150 PSI

I don't have a leakdown tester in this garage.  Dang it. 

Well, if the not running right has anything to do with coolant getting into the cylinder then you can definitely just visually observe it. Put a socket on the crank and spin it around until cyl6 is coming up on the exhaust stroke so you can look past the open valve, repressurize the cooling system and let it sit. If it's leaking into that cylinder you should eventually get a puddle visible through either the valve or the plug hole. I would go past 12psi, personally. I go up to 17psi pretty regularly and can't remember ever blowing an otherwise-good hose up. I do sometimes find bad connections and have to pressure down, reseal and pressure up again,  and i consider that a good thing. 

Is this a reman or one of the GM replacement engines?

ATK reman long block.  I may have found my issue.  Slipped valve cover gasket, and oil that has a green tinge due to the paint marks on the head bolts.  Maybe it's oil after all...

In reply to Kramer :

Most remans I have seen lately had their oil systems primed/pressure checked with oil that had fluorescent dye in it so they could quickly see leaks.  It will look greenish in daylight.

Knurled. said:

In reply to Kramer :

Most remans I have seen lately had their oil systems primed/pressure checked with oil that had fluorescent dye in it so they could quickly see leaks.  It will look greenish in daylight.

This may be the case.  I'm using conventional antifreeze, so it's darker green than extended life. And the drips I've been getting are very green.  So much that I didn't really check to see if it was oil. 

I'll reseal the VC gasket and reinstall it.  And quit worrying.  

Then I need to determine if the rough-running issue is from bad gas.  Dual tanks are full of Eastern Oregon gas, so good chance it is bad after four years of sitting.