The fix was this:
Butterfly valves in the manifold had tiny screws that had come out over time. Engine ingested one but seems OK. Another 2 were about to go. All cylinder pressures good. I removed the entire butterfly assembly that seems to help with idle and cold starts. Only problem this causes is infrequent rough idle sometimes... no ryhme or reason why I've been able to find though.

This is likely why so many of these 3.8 liters are blown up before their use is full. Ingesting screws into cylinders is not ideal! Very dumb design indeed!

 

Glad you were able to catch that before it became a bigger problem.