Personally I would be looking at that crankshaft to see if it's a cast iron instead of a forged Steel and if they put a neutral harmonic balancer on it.
That is actually possible. The fact is you don't know the history of the build and therefore you are on a witch hunt. I hope this would not be the case but you never know.... Unless someone gets lucky this type of problem could turn into going through the complete drivetrain....
