If it's got grey oil that sounds like something has been mixing with the oil?? Did they guy add something to the oil? A clogged oil cooler doesn't stop oil flow it stops or severly slows coolant flow thus overheating the oil that flows under it. I would start at the LPOP and check to see if it is plugged up or something is stuck inside it. Also might want to pull the oil pans and check the LPOP pick up tube and see if there is anything out of the ordinary in the pan.