[Barry_R]

You answered your own question. Really rich running will fill the oil with fuel. Fuel is a poor lubricant, but you're also not putting any load on the engine. Load and the resultant cylinder pressure is what seats the rings. Eight hours is a very long time to run an engine with no load. On our dyno work we'll rarely give the engine more than 30 minutes before WOT pulls, and even during cam break in I will cycle moderate load into the engine - something you cannot do in the car or on a stand.