Do you have a crankcase oil leak on the top of your 7.3 liter Powerstroke? It may look like a leak coming from the rear main crank seal since the engine valley has a drain and oil will drip out of the inspection plate between the engine and transmission. This is not a common spot for the HPOP to leak from, but this O-ring will correct the problem if it is leaking from the back plate. 

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