The Mythical 7 Cylinder V8

Back in the eighties working at a Ford Dealership had an F150 4.9 I6 come in using oil & missing less than 10K miles... #5 plug covered with oil... Back side of intake valve was clean, Pulled the engine & tore it down... No rings what so ever on #5... Stuff happens... Missing Piston? Hard to see that getting out the door...