Troubleshooting Head Components

If that was in my shop, I'd position the pistons in a manner to be able to pour an inch or little more of clean solvent in each cylinder.
See how long it takes to drain a cylinder.
I wouldn't be surprised if one or two of those lost fluid very quickly, and some way later, some may hold fluid till next day.
Compression test of sorts.
If all are fairly even after a while, hours/overnite, send it.
Draw your own conclusion .