Obviously something something is amiss with the oil return pump system!!!
I'm not real familiar with pumped turbo oil returns,but I have had some experience with Turbo Charged engines!!!Turbos are bad to get coked up in the oil return lines and cause oil pumping through the engine!! The oil is dark back there because it has been run through the induction system and cylinders of the engine!!! This also could be caused by bad seals in the turbos,and this would be my guess!!!! It is very important to let a turbo engine to Idle for 1-2 minuets before you shut the engine off!!! Even just driving it easy with out boosting the turbo is ready to boost and the impeller is turning 50-100,000 rpm's!!! If you roll in off the street and just shut it off,you have shut the oil off to the turbo and it still is turning those kind of rpm's!!! So it is very important to just let it idle and settle down a little so it won't run out of lubrication before it stops!!! Some set up's have a pump that send oil to the turbo for 30- 90 seconds after the engine is shut down and this will eliminate this problem!!! I hope this helps and they can get it worked out for you!!
PS Synthetic oil will burn in a engine with little or no smoke!!!!