Isx cm871 turbo issues

[Doodles_mmr]

I'm having some issues with my cm871. I'm on the second turbo and it is same problem as last time about a month apart. It's leaking oil out from behind the compressor wheel. These are cummins reman chargers. Truck has been demandated for about 3 months now. This truck has had multiple issues since then. The shop that worked on it says only way to fix it is remove vgt turbo and replace with a standard old school turbo. Everyone has told me this was wrong. This is one of my fleet trucks and driver has been off work and I'm at my whits end on what's actually wrong with it. Also getting since demandated are Intermittent code and derate for sensor supply voltage low. Measure around 3 volts on that part of the harness then can disconnect batteries for about 15 mins plug back up measures at 4.85 volts. Any help will be greatly appreciated. I'm about ready to pull my hair out.