200 coolant leak in head after rebuild?

Got it back together but noticed a small coolant leak in head casting. It is between 5 and 6, first pic to get you an idea of where, the second pic shows a small valley in the casting between head bold and inj line. Does not leak until started. After starting you can see the crack percolate a bit then turn green with coolant. Does it with rad cap on or off while running. So...is this head junk? Can it be J B welded? Stop leak? Or bite the bullet and get a reman. The only thing we did to the head was a good pressure washing while the rest of the engine was a complete overhaul due to sleeve o ring leak. Really don't understand why this came to a head right now, unless we took 50 years of crud off head giving it room to breathe.