No oil flow mystery

Charrlie_S said
Remove the oil pressure sender, and crank the engine (filter on). See if you get any oil flow. If no, problem is in the pump/filter area. If yes (might be reduced flow) problem is internal. The main oil gally has a threaded plug in each end. If the rear plug is left out, oil will run out the bell housing area. If the front plug is left out, the oil will stay inside the timing cover and run back into the pan.
EDIT: Did you try a different filter?

We have not tried a different filter, but hearing about that second plug behind the front cover is one of the things I was hoping to hear about. If they can forget to put the back plug in they can forget to put the front one. I'll have to pull the harmonic balancer and timing cover to see