Magna-fluxing found a Crack in one of the heads

When I pressure test a cylinder head. I use a plate that covers the gasket surface and plates that block the ports for the coolant that goes into the intake, then just add 40psi of shop air and apply a soapy mix and look for bubbles. cracks between the intake and exhaust seats don't always leak but they can expand at anytime. I have drilled and tapped holes through the crack and installed special screws called Lock & Stitch. Then you install harden seats in the intake and exhaust this will fix most cracks but it is very time consuming if you can find a head it maybe cheaper. Good Luck