Sudden Excessive Oil Consumption

I have an N14 Cummins with 979,000 miles on it. I had an injector tube leaking, so I had a 6 pack of injectors put in it, along with a reconditioned head, this engine has given me absolutely no problems at all, except normal wear and tear.All of the sudden, I'm going through a gallon of oil every 1,500 miles, turbo was replaced 2 years ago, could it still be that? I have noticed some oil coming from my exhaust, and spilling out from the flex tube from the back side of the turbo going to the muffler. I do a lot of idling, and recently found that I have a small amount of oil on the ground right directly under the flex tubing behind that I mentioned earlier. Could it be the turbo? the bearings washed out because of the injector tube leaking? Or something else? Any ideas? NOTE: This engine was using 1 gallon of oil every 7,000 miles up until this latest problem