The only time I saw this happen was when the rear main was put in upside down.
When you do that the oil holes are covered and no oil goes to the #6 rod. You would be surprised how long a GMC will run with know oil.
I understand that one of the military tests was to drain all the oil out of an engine (like the pan was shot full of holes) and see how long it ould run and the GMC was better than any other engine tested in the late 30's and early 40's and the military chose it.
