Here's one more vote for the Motorcraft glow plugs ONLY!!!!!!!!!!! I had a glow plug tip on injector 8 fall get stuck in the head because of swelling and it was the only one in the engine that wasn't a Motorcraft. Somehow that tip was pushed down into the head farther than the position it sat in the head at the original installed depth. Was probably making contact with the piston at some point. It was an Autolight. That engine is since gone bye bye and I'm currently installing a reman. Ford 7.3.
I wanted to tear down the old engine to find the source of it's demise, but I had to return it ASAP for the purposes of getting my core deposit returned.