Tell us how you removed the anaerobic sealant prior to installling the new injector cups?
Sounds like classsic ultra slow pin overnight coolant circuit leak, down the verticle side of lower lip of brass to iron contact surface. That sealing surface then transitions into a horizontal sealing surface before the combustion chamber.
Why does it pay 18 hrs. bcause ford wanted to ensure a service proceedure that would ensure the "collective" service end proceedure. This was by having the heads on the bench.
No residual trash and full visualization of all surfaces for residual sealants or hydraulic boring ( grooves running vertically on the iron surface.
Why why why? To be able to visullly inspect during proesss. Not expect ".everybody" to be able to get alllllll the way in, doing the funky chicken just trying to do what you all did, let alone ensure that full visualization of the head's injector cup is....PROPERLY PREPPED. We will get back to that...
The pros come on with our "pracitil" alternatives. Over time..Assumptions of basic knowledge and the required steps and precautions are made, threads read and it leads to at times to poor to disastrous results.
I'll shorten it up.... when doing the funky chicken with probably a HPOP tank or other in your chest, don't know what's going on with forearms planted in some iron or a "$125 ICP sensor you are trying not to snap off,,,but you were using a top side creeper hovering above and using a bore scope to ensure all anaerobic sealant( the Loktite glue in bottom of head's injector cup bore) from previous installation of brass cup,,,,,was not left there in a state of pieces of uneven old pieces of plastic,,, before you drove home a new injector cup on top of said anaerobic sealant remains.", right?
Get somebody to stand close to the tail pipe after an overnight soak ( no pun intended ) to tell you how the antifreeze smell was.
I would lay money down