Water on top #4 3.0

Have a '96 3.0. Water on top piston #4 , pulled head and manifold, manifold had visually crack on outside below carb. Over 3 and 4 cylinder. Pressure tested manifold. With plate over elbow mount , with pressure tester at water elbow from thermo. housing 18 psi and it held , I know if I heated manifold it would loose from visable crack on out side. Checked head for cracks no visible cracks near valve seats or in intake-exhaust ports. No visible blow out of head gasket. No visible cracks in cylinder walls (water on top of piston) put bact together new gaskets, customer didn't want to pay machine shop to look at head and resurface. Which in my opinion is a no-no . cranked engine this morning ,ran great no skip, got it to temp. Shut down motor to change oil( because of mix) put new oil in, pulled#4 plug turned motor over and of course water fine spray. This is the head with the smaller exhaust ports. Hard to find , Michiganmotozr wants $618.00 for head. I did use permatex copper spray-a-gasket on head gasket. Any advice would be appreciated
Is this a common , known about situation?

Replaced manifold

Found that it was a crack above exhaust seat on #4 cylinder had to remove valve. Fixed , though head was hard to find. That was a week after original post