Well it has been one long day. I was stuck at the shop the entire time. I kept thinking it was just going to be a short while before it was fixed, and it kept going on and on.
So first off they tried the resistors, no change. They put the car on the lift and started working towards removing the downpipes as I was ready to give up. I had Riss on the phone at the time and they were throwing a bunch of information at me, and then Stett found an obvious problem. The intake line leading to the rear turbo had come off. This most likely occurred because I had spent so much time working on the rear connection of the intake in an effort to move the intake further to the rear of the engine to line up with the plenum better and have plenty of clearance. This is the source of the oil as well as the hesitation and rough idle and would also throw the same codes as the rear O2 sensors.
It's important to note that the SES light had never come on until shortly after the downpipes were installed. So I believe this connection finally came loose after the pipes were put on, possibly while I was out Friday giving it a bit of a good run to break in the downpipes. It must be one of those bizarre coincidences that really threw us for a loop.
So that took a long time to fix. Here is part of the process:
The manual says to remove the downpipes to access that connection, but they did it without pulling them out. The car runs fine now.
However the codes remain. Either the O2 sim is bad, or it's not in right. I will be checking it later myself.
They happened to have an N54 turbo lying around and I thought some might enjoy seeing exactly what they look like:
